Heating & Cooling Thermostat FAQs.

Questions & anwers about how to install, set, troubleshoot & repair home page: this article series explains selection, installation, use, setting, and adjustment of heating or cooling system room thermostats or "wall thermostats".

This article series answers most questions about central heating system troubleshooting, inspection, diagnosis, and repairs.

Thermostat FAQs

These questions and answers were posted originally at THERMOSTAT DIAGNOSTIC GUIDE - be sure to see that article as it's the starting point for diagnosing and fixing problems with heating and cooling thermostats in buildings.

On 2019-10-03 by Ralph Teasley

Trane Thermostat and Thermometer has a high rated voltage running on Trane to wall at 905 Hilton Road Anniston, 256-237-9135 call Ralph please.

On 2019-08-18 by (mod) -

Alice

A simple diagnostic that can rule the thermostat in or OUT of the problem equation when an A/C system won't run is to simply remove the thermostat at the wall and short together the two cooling wires that should turn on the A/C. After all, all the thermostat's doing is acting like an on-off switch.

There can be a delay in turning on the equipment that's actually normal - depending on the exact situation.

We also do this same test right at the A/C control at the air handler or at the compressor/condenser unit (depending on where your thermostat wires go) - that can eliminate a bad thermostat wire itself or a break or short in the thermostat wiring.

On 2019-08-18 by Alice

Left for vacation for a week and set wifi Honeywell TT to 79. Came back and cooled home to 76. Next morning, TT showed the room and the 'set' temp at 76. Turned down to 75, as the day is heating up house quickly, but nothing happened. Put fan on manual, and it works. Went outside to A/C unit, and poked at it, banged on it (like that would actually do something ;) ), but nothing. turned TT down to 73; still nothing.

Reset the TT by removing it from the wall (which I have to do frequently now or it loses its wifi connection). After starting to go to my neighborhood FB page to ask for HVAC service recommendations, the unit turned on and seems to be working, but it took at least 5 minutes from the point of turning the TT down to for it to kick in. It now seems it takes longer than normal to kick in when I change the temp.

Are there any ideas or future troubleshooting tips for a DIY person where the only HVAC experience has been to change my thermostat? Should I be concerned? I've lived in the house for 5 years and so don't know how old the A/C is, but replaced the furnace two years ago. Many thanks - Alice

On 2019-02-09 by (mod) -

T

Did you connect the red & white at the thermostat? If so try jumping the thermostat terminals at the furnace at the other end of that same pair of wires.

\Still no heat? Could be a damaged relay or control board.

On 2019-02-09 by T

1 furnace, 2 thermostats. Upstairs TT works, downstairs TT a/c and fan (not on auto )work. Recent power outage. Connected red and white wires to each other, no heat. I have a Ruud furnace. Everything worked fine before power outage. Do I have a switch somewhere that needs to be reset?

On 2018-12-20 by (mod) -

I'm not sure, Ed.

Check the diagnostic suggestions at https://inspectapedia.com/heat/Furnace_Fan_Wont_Stop.php FURNACE FAN WONT STOP

There could be a control board issue, a dip switch setting, a too-long purge cycle at the end of a heat-on cycle, even an intermittent or loose thermostat wire.

On 2018-12-20 by Edward Nickisher

My hvac system will work fine for heating then start blowing cool air for no reason,if i turn it of at circit breaker overnite then turn it back on in the morning it works just fine this has been going on for some time,whats the problem.ps filter is new.thx.

On 2018-12-20 by Karen

My Trane Comfort Link II thermostat has error message 126 but the heat seems to be working fine. What does this mean?

On 2018-12-11 by (mod) -

Purge

As we don't know the brand and model of your gas furnace I cannot give a detailed guess at your heating problem and have to offer a general reply.

At the end of a "heat on" cycle a furnace continues to run for a short time to remove the remaining heat in the furnace heat exchanger - otherwise the steel could overheat when the fan stops and the heat exchanger could be cracked or damaged, rendering the heater unsafe.

That process is described at https://inspectapedia.com/heat/Furnace_Fan_Cycles_After_Heat.php FURNACE FAN CYCLES AFTER HEAT

There are other types of "purge fans" used in heating equipment, in part because the phrase "purge fan" may be used incorrectly or inconsistently.

For example some direct vent furnaces require a fan to force combustion products out of the exhaust flue, and other furnaces or heaters may use a draft inducer fan to assure adequate draft in a tall or cold chimney.

Sorry but I don't know enough about what your system is to say more.

I do not think a novice should try to fix the exhaust venting fans, blowers, or equipment on a furnace as indeed a mistake could risk a fire or even fatal carbon monoxide poisoning.

Attach a photo (one per comment) of your furnace, brand, model, data tag, and of the "purge fan" under discussion and we may be able to comment further.

Let me know what the heating service tech tells you - what we learn may help keep others safer.

On 2018-12-11 by "Purge fan seized up"

My heater all.of a sudden stopped heating. I called the gas company and they sent some one to look into it. He spent some time diagnosing and figured out that the "purge fan" isn't spinning and it should be, and advised that I call an appliance repair person. I'm waiting for a call back, but, what is involved in identifying cause and repair options. Do you have a sense of how likely is this fix to kill me financially? Is it something I can use YouTube to help me fix myself, or if this something a novice shouldn't dive into?

On 2018-11-25 by (mod) -

Andre,

Thank you for asking interesting question. That's a condition that I have not encountered. Normally when a thermostat display goes blank it's because there's a loss of power to the device. I would start by checking the electrical connections on both ends of the thermostat circuit.

As a very speculative guess, it's also possible that a low voltage Transformer on your system is overloaded, that is being asked to power too many devices.

On 2018-11-22 by Andre

I have a 2 zones heating/cooling. Evrytime the heating srart in zone 2 the zone 2 thermostat (this is connected directly to power) goes blank. When the heating stop the zone 2 thermostat turn back on.
My zone 1 work fine.
What can cause my zone 2 thermostat to go blank?
Thank you

Question: "Filter" message on thermostat

May 26, 2014) Igor said:
Question: My thermostat show "filter", what is that?

Reply:

Igor it's telling you it thinks it's time for you to change an air filter.

If your system uses hot water heat, not hot air heat, then you can ignore the message.

If your system uses forced warm air for heat, try changing the filter.

Watch out: some HVAC systems actually monitor air pressure in the duct system and can detect when the air filter has become blocked. Changing a dirty air filter is very important for effective heating or cooling and dirty filters can cause complete loss of either heating or cooling.

See AIR FILTERS for HVAC SYSTEMS

Question: my thermostat does not respond properly to room temperature

(May 27, 2014) mike said:
My capacitor, contactor and thermostat have been replaced today by me correcting the issue of the fan compressor not coming on and now my air handler fan comes on for 2-10 minutes before my fan compressor unit kicks on and then the air handler fan stays on 2-10 minutes after the fan compressor unit shuts off. Ive also noticed on the TT the unit is running to a temp lower than the temp setting by 5 degrees. Ive looked everywhere on how to calibrate the setting but cant find info. The room temp showing on TT is correct but is disagreeing with the set temp for activating unit off and on. is it calibration of thermostat or something else?

Reply:

Mike

In the article list In the ARTICLE INDEX found among the Continue Reading links at the end of this article you can see articles on

THERMOSTAT CALIBRATION
and also an article on the
HEAT ANTICIPATOR

but your thermostat may be keeping things running past the set temperature for other reasons - like its location.

Check the room temperature shown on the thermostat against the set temperature on the thermostat.

Question: water drips onto heating or cooling controls

(Nov 8, 2014) Dan J said:
Having a problem with a 5 zone hot water system.

4 Heating zones

1 Indirect water heater

One of the heating zones will call for heat, the furnace will cycle, but does not run long enough to heat the water properly.

All of the other zones seems to be working properly. If a 2nd zone calls for heat, while the problem zone is circulating the furnace will fire and run properly.

The only way I can heat the problem zone is to ensure a 2nd zone is calling for heat as well.

I swapped thermostats between the zones and still the same problem only with 1 zone.

Any ideas.

(Nov 9, 2014) Dan J said:

Solved my problem. A shut off valve had a very minor leak that was dripping into the zone valve.

A shut off valve had a very minor leak that was dripping into the zone valve.

The connection to the furnace heat side would work until a small amount of water got onto the connections.

Hence the weird and inconsistent problems.

Quick turn of a wrench and the problem is solved.

Reply:

good going Dan J - indeed dripping onto a control shorts electrical components - you may need to replace the dripped-on zone valve head.

Watch out: if the electrical components of the zone valve were wet then soon you may find that corrosion has made the valve inoperative- the control head may need replacement.

Question: A/C blower making loud sound - doesn't respond to the thermostat properly

My ac blower was making a loud sound so it went bad i replace it with a new one and know the thermostat is not working properly the setting on the thermostat it

works wrong when i set it on the auto and cool it does not turn on the blower when i set it on fan and cool it works

but it does not shut off i change the thermostat and it does the same thing. Do you know what it could be? - Angelo 8/5/11

Reply:

Angelo I'm not sure but most likely there was a wiring change needed, or perhaps someone shorted a control board or relay

Question: A/C freezes up after blower was shut off - compressor doesn't stop

Recently my A/C began to freeze up after the blower was shut off by thermostat at right temp, I noticed that the thermostat would shut off the blower but not the outside unit causing it to keep running and freeze up the inside coils, but when I turn thermostat to "ON" and just let it blow, it keep running and getting too cold.

How do I find out what is making the thermostat only control the inside unit. - Kewl Jungles 8/8/11

Reply:

KewlJ
It sounds to me like a control problem - it's odd for the compressor/condenser to keep running after your thermostat says the indoor temp is satisfied.

I'd ask for an HVAC service call to check the thermostatic expansion valve and the A/C control board circuits. Let us know what you're told - it'll help other readers.

Question: Inadequate cooling, tech says just keep running the system

We just had evaporator coils replaced on both a/c systems. One system has been cooling fine ever since. The other only seems to cool at night.

The thermostat seems to be working OK and the air coming out of the vents is cool although perhaps not quite as cool as that coming out of the vents driven by the other system.

The system that not working correctly gets to be six degrees warmer than the set temperature on the thermostat.

The company that installed the new coils came back and just checked pressures at the condenser and said everything seems to be working OK and that it may take some time for the everything to cycle through the new equipment.

Any suggestions of problems that may result from new coil installation or what else could be causing the problem? Mike

Reply:

A/C equipment does not normally need a "break-in" period to begin working properly. In fact about the only thing that leaving the equipment running will accomplish is that it lets the technician get in her truck and get the heck out of there.

An exception might be a response to an owner who complains that the house is too hot or too cold when the system has been just turned on

. If the heating system is indeed producing output air at normal heating temperatures or cooling air at normal cooling system output temperatures and air flow rates, then indeed time may be all that's needed to get the building to the desired temperature.

There are a number of explanations for inadequate cooling, including in a new installation (where we figure we don't have blocked air filters etc) improper refrigerant charge, or a refrigerant metering device not working properly. Call the service company and ask for help from a more experienced technician.

Mike:

A cooling system that works only at night suggests that it is not producing enough temperature drop across the cooling coil, or it's working so hard during the day that a control is failing or the coil is icing up.

The line about needing time for everything to cycle thorough the equipment is not a diagnostic I understand.

When coils are replaced on an A/C system it's easy for contaminants to enter the refrigeration piping system, compressor, and controls. Debris can clog a thermostatic expansion valve or cap tube, resulting in improper system operation. The installer usually pulls a vacuum for some time on the system to remove as much debris and moisture as possible, then installs one or two filter/dryers on the refrigeration piping.

Question: My A/C blows warm air for a while before cool air comes out

when I turn the air conditioner onto heat it blows out warm out for a few minutes and then cool air, would this be the thermostat or would it need gassing, it is just over five years old. - Marylin 3/14/12

Reply:

Marylin, if the air produced by your system is adequately cool after the initial warm air delivery I suspect your building may have poorly insulated ductwork running through a hot attic of some length. The hot duct is warming the initial airflow.

Reader follow-up:

Hi Dan, if it was the ductwork wouldn't it have played up by now i have had the unit for just over five years, when I go downstairs to the main unit and touch the pipe it is hot,but we just cant seem to get enough heat upstairs..

Reply:

Yes Marylin I agree - that's part of the difficulty of guessing at a question with not much information. However depending on duct type, routing, condition, insulation can fall off, be torn off by animals, or open and leak - it's worth a careful inspection in any case.

You describe initial warm air followed by cool air from your cooling system supply ducts. Is it always the case at every "on" cycle?

Or only when the system has been off for some time? We're trying to sort out whether the air handler or piping or other components are just warming up and warming the initial air, or whether there is a delay in startup of the cooling compressor. Working with an accomplice turn down the thermostat and see how quickly the outside cooling compressor starts up and whether it's starting normally or with buzzing, humming, a delay.

Question: why won't my fan work on AUTO

(Nov 11, 2014) Erick A. said:
My Home’s Setup:

- Honeywell RTH2300 / RTH221 series wall thermostat

- Payne gas furnace (PG8MAA) - 5 years old

- Three wires hooked up to the Furnace Control thermostat terminals -> G, R, W

- Those wires are hooked up to the corresponding terminals in the thermostat (G, R, W)

- Fan operation switch set to “Gas or Oil”

Problem:
If I change the thermostat’s external fan switch to “Auto,” and crank up the temperature setting well past the current set temperature, the furnace will not produce any heat (doesn't fire up at all). However, if I change the thermostat’s external fan switch to “On” and repeat the same step above, the furnace works as expected.

What is causing the “Auto” fan setting to fail?

Reply: What is causing the “Auto” fan setting to fail?

Erick it sounds to me as if the thermostat is not wired properly.

In AUTO mode the fan should turn on when the limit switch senses that the plenum temperature is at or above the FAN-ON setting.

See FAN LIMIT SWITCH in the More Reading article links above.

Question: can a heating + cooling thermostat fail in just one of those modes?

(Jan 5, 2015) Russell said:
Can a central unit thermostat that controls both air and heat have one side not work but the other does

Reply:

Interesting question, Russell, for which my answer is yes.

Typically a thermostat that controls both heating and cooling is connected to additional wires for the cooling circuit - either of which could be shorted or broken, or an internal fault in some thermostats might mean switching from heating to cooling may be unsuccessful. I'd check the wires first.

Question: Trane AC runs continuously - why won't it stop?

(May 14, 2015) Anonymous said:
My parents purchased a Trane AC in January 2015. Since the Spring, the AC continuously runs, even though the thermostat is set on 70 degrees. We were told by the local dealer where they purchased the unit, that it would stay within 3 degrees of 70 degree. However, the thermostat will actually read 75 and it will be as low at 59 degrees in the house and the AC continuously runs.

They have replaced the theromstat and even put insulation behind the thermostat and it still runs non-stop. Up until this morning, it only did this in the evening-around 5:30 pm EST to 7:30 pm, then it would stop running and warm back up. This morning, it's actually in the 60's outside, but the AC is running continuously and it's 61 degrees in the house.

The local dealer doesn't have any idea what's causing this and stated they may need to move the thermostat. Please help!!!

Reply:

Anon

If the room temperatures reach the set temperature on the thermostat then the AC unit should stop

. IF it does not, then there is a problem to be found and fixed, such as shorted thermostat wires or a bad control relay or circuit board. See see THERMOSTAT WON'T TURN OFF in the suggested continue reading links at the bottom of the article above.

If the room temperature never reaches the thermostat set temperature in cooling mode then there's a different operating problem to find with the AC unit - standard procedure for any trained service tech.

See DIAGNOSTIC GUIDE A/C or HEAT PUMP

Question: Gemtech GT110D thermostat not working

(Mar 2, 2015) Joe said:
Hello, I need some guidance here. Turned on the A/C unit, and discovered it was not cooling after about 30 minutes.

The A/C unit did come on. Went to the thermostat and checked it and realized the display was not working and that it had stopped along with the a/c.

I shut off the breaker to the unit, and then proceeded to open the thermostat and take the batteries out when I discovered it did not have any batteries. Is this thermostat running on hardwiring only?

Is that why it does not have batteries? What do I do next?

Reply:

If the thermostat is dead that suggests power is off at your heating system. Also check / change the thermosat's own batteries.

Question: Florida system not cooling

(Jan 24, 2013) Wayne said:
The outside fan is working. The inside air is blowing adequately, but the air will not cool, nor will the heat turn on.

Could this be a thermostate issue or something else? It is a digital TT. Nothing with the system has been changed. I've checked breakers. It is "winter" here in Florida with 65 to 75 degree daytime temps. System is old, 1991.

Reply:

Wayne,

I'm a little confused - you say everything runs but that the air won't cool AND the heat won't turn on. Are we looking for heating or cooling.

Watch out: do NOT keep switching between heating and cooling - doing so too quickly can give the compressor a hard time re-starting.

If all of the equipment components start and run you should feel air coming out of supply registers. If in COOLING mode the air never cools then I suspect a problem with refrigerant or the refrigerant metering equipment. Search InspectApedia for air conditioner repair.

If in HEATING mode and air is delivered but it is not warm coming out of the supply registers and you have a heat pump system the I suspect the same.

If in HEATING mode your system is designed to switch to an alternative heating source, or to backup heat, that sounds like the trouble area; Make sure your Thermostat is set to HEAT.

Question: Honeywell programmable thermostat troubleshooting

(Jan 28, 2013) Liz J. said:
My thermostat for the heat is set to 62 degrees on our second floor all day and night (we have zoned heating). T

he thermostat temp shows that it is reading the temp at 70,but the heat comes on anyway. The thermostat didn't always behave like this, but it's less than a year old - is it possible the thermometer is faulty?

It's a Honeywell 7-day programmable thermostat (RTH7500D). I'm not sure what else the problem could be.

Reply:

Liz:

First check that the thermostat is not in HOLD mode at a different temperature than the 62 degrees that you want. Let me know what you find.

If the TT is actually calling for 62F and room temperature is at 70F, AND heat is coming on in that room, then there could be a short in the thermostat wires - if two wires are shorted together it's the same as the TT calling for heat.

Question: Hunter thermostat display flashing "2"

(Jan 31, 2013) Carissa said:
My hunter thermostat is flashing a grey square with a white number 2 on the left aide of the lcd screen

Reply:

Carissa,

IF a Hunter thermostat is flashing a "2" error code that may indicate that it needs new batteries. Try replacing the batteries and then resetting the thermostat to clear the error. You may need to insert a pen tip or paper clip into the reset opening on the thermostat.

If you don't have an owner's manual for your thermostat contact Hunter Thermostats - their website is at hunterfan [dot] com/thermostats

Question: White westinghouse AC won't turn on - code En

(Feb 1, 2013) Sherman said:
i have a white westinghouse windows type which wont turn on - single beep then error code "En". What could it be?

Reply:

Sherman:

I don't know what an En code means on a Westinghouse A/C unit but there are some obvious things to check. Start with the owner's manual. Fault codes are usually listed there.

If you don't have that booklet, tell us the model number and we'll dig it out for you.

Also, White Westinghouse window A/C units are sold through Sears - so if we can't resolve this En error code you can drop by any Sears store to leave your unit for testing and repair - less costly than hiring a tech to come to your home.

Question: blank display & other thermostat troubles

(Feb 7, 2013) Don said:
I am a homeowner with no HVAC knowledge. I'll probably use incorrect terminology but here's my problem:I have a dual zone heat and air system with two separate thermostats.Problem is that the screens go blank on both therms at the same time and will not control the system.

Stays blank for a few minutes (15-30 minutes)then comes back on and works fine for a week or so (happening more frequently now) when the thermostats come back on they re-set the temp to 68 Degrees.

Do I need new therms or new low-voltage transformer?

I don't understand why both therms go on the blink at the same time unless they are controlled with a single (bad)transformer.

Final question...can this repair be done by homeowner or do I need an experienced repairman ? Thanks, look forward to your response, DON 2/7 2013

(Feb 13, 2013) Kathleen said:
We have an old gas fired boiler, and plan to replace it in the spring.

Meanwhile, it loses pressure and the top floor of the building loses heat.

There is not an obvious leak, but some visible weeping and corrosion in the very old system.

We've just had the pressure adjusted (again) and wonder if everyone in the building (4 condo units in 6 floors)leaves their thermostats alone (in other words does not lower them at night) will that help maintain the pressure?

We have Honeywell programmable electronic thermostats, model RTH230B. One (we have 4 zones) displays "filter." Does this refer to a filter on the boiler, or on the thermostat itself?

(Feb 17, 2013) Mary said:
I used water and soap on a tissue to clean the Honeywell thermostat screen and I believe the tissue also had some hydrogen perioxide on it. The tissue was quite soaked. Now the screen is frozen. Would the moisture cause problems in the circuitry?

(Feb 26, 2013) lea said:
my thermostat in my house i turn-on AC but I feel air blowing only I don’t feel AC on Please me .

(Feb 27, 2013) my home thermostate said:
I felt cold when i woke up and went to look at Thermostat and it said low batteries so i put new ones in and now it is showing a black screen and doing nothing. what could be wrong with it?
Do i need to use the exact batteries that it ask for?

Reply:

My home

If the thermostat still shows a black screen (this is an LCD or electronic thermostat, right?) then I suspect the new batteries are themselves bad or are installed improperly.

Question: Honeywell TT won't start the AC, heat nor fan

(Mar 4, 2013) Bob Humid said:
Honeywell TT will not start a/c, heat or fan. Found no voltage received from transformer.

Test showed zero on high voltage side and resistance to wires on TT wires side. Deemed as bad and replaced. Everything worked fine but transformer had continuous noticeable humming sound, so I exchanged it.

Everything seemed fine till noticed next morning inop again. I changed the 24v coil but hate to install another transformer for fear it might blow again if this not the right fix. What other parts need to replace to avoid blowing transformer?

Reply:

Check for an open TT wire or lost connection;

Question: backwards wired thermostat ?

(Mar 8, 2013) Mikal said:
If I have a mechanical thermostat that closes when cold to heat and opens when it reaches desired temperature, how can I reverse it to use it for a cooling device to open when I achieve a certain cooling temperature?

Reply:

Mikal

If your thermostat has a switch indicating Heat, Off, Cool, then it supports two more wire connections intends to run a cooling dvice. If not, because the switch makes (closes) on temperature fall and breaks (opens or turns the circuit off) on temperature rise to the set point, it won't work for A/C.

It'd be backwards.

Question: question from HVAC school student

(Mar 20, 2013) Vincent said:
this is a question as i am in school for hvac and i cant figure out this question. An existing home has and oil furnace with no AC. Explain what components and wirimg you would have to add to the existing furnace for the air conditioning to work? help???

Reply:

Vincent,

Your question asking me to do your homework is something for which I have sympathy but it's a bit much. Take a look at your textbook: for converting a forced hot air heat to add air conditioning we need a lot of stuff:

Outdoor compressor/condenser unit
Refrigerant piping
Indoor Cooling coil added to the air handler
Indoor thermostat that provides cooling control
Indoor air handler adjustment or replacement to the blower fan - often to go to a two-speed fan;
Possibly some duct or supply register changes.

If you search InspectApedia for "Air Conditioning Retrofit" you can find more details as well as some SNAFUs to avoid.

Question: loud BANG and electric heater fire worry

(Mar 20, 2013) william mcdonagh said:
loud bang woke me at 3:00 a.m. last night , two 500 watt inwall fan electric heaters one was red glow with small flame , turned wall thermosat off red glow and flame disappeared checked and monitored situation for 2-3 hours incase fire behind wall . removed wire from wall thermostat to disable faulty 500 watt wall heater .

other heater now works fine but the odd thing is before thermostat was (21c to come click on 16c to hear click off ) now (31c on / 26c off ) .

Reply:

I agree that this is dangerous and you should leave the equipment OFF while waiting for a service call.

William,

You are describing what sounds dangerous to me, and also it sounds as if you did the right thing to turn off and leave off any suspicious equipment. However I also worry that if there was an electrical fault that was an overcurrent (which may not have been the case) the circuit breaker or fuse should have tripped.

If there was no overcurrent then perhaps the problem is that a controlling thermostat is not working in the bad heater.

Leave it off until you have it replaced or repaired.

Question: humming noise at Trane HVAC unit

(Mar 20, 2013) Natasha said:
We have a Tran Central Heat and Air Unit I have noticed lately that the little green light will be on that shows the heat is on and u can hear a humming noise but the fan isn't blowing any air.

To adjust the temp on the thermostat u slide a little tab at the top of the box. When I take the temp low enough that the heat would kick off and the light goes off then slide it back up to where the heat will kick back on then most times the it will come on and blow normally.

Heats fine it the next day or so and I notice its getting cold in the house and I look and the light is on but no heat blowing...I usually keep the heat on 73..

.lately I have been having to put it up to 75 to keep it warm...tho it had been pretty cold this winter. . Sliding the temp up higher doesnt do anything just sliding back down below 70 then back up to 75...then she kicks on and works fine...Do have any idea what's going on?

Reply:

Natasha,

A Trane heating/cooling unit whose fan doesn't come on and that hums sounds like a bad fan motor or possibly a bad fan relay in the air handler.

This is a good reason for a service call. Your heater may have a fan motor that is having trouble starting; a hard-start capacitor might get some more life out of the blower fan assembly.

Question: are wall thermostats required?

(Jan 23, 2014) Jean Bayliss said:
Is it a legal requirement to have a wall mounted thermostat when having a
new central heating system installed?

Reply:

Jean

"Legal requirement" is a bit of a stretch.

But since a central heating system will not operate without one or more room thermostats, and since omission of a thermostat would most likely violate the manufacturer's installation instructions, one could argue that such an installation is not "code compliant" (since building codes typically require that the manufacturer's instructions be followed).

What on earth is going on? Who would install a new heating system without a control thermostat? Perhaps your installation is controlled by another means such as a wireless or remote-control room thermostsat?

Send along photos and documents (see our CONTACT US link at page top or bottom) and I may be able to comment further.

Question: furnace is cycling

(Jan 23, 2014) Vic Hoefer said:
I have a furnace that cycles constantly. It will come on for 30 to 40 seconds, shut off for 90 seconds, then come on again. This happens non-stop. Could this be the thermostat or maybe a relay problem?

Reply:

Not sure Vic. Watch the fan limit switch as the furnace cycles. If the limit switch is rotating to the high cut-off temperature and then shutting off the unit I'd first check for a dirty air filter, blocked HVAC duct or dirty blower fan, or inadequate return air.

Question: warm air not warm enough

(Feb 10, 2014) Zenia said:
My HVAC unit is dual Fueled Main source of heat is propane gas as emergency the heat pump. Warm air flows but never reaches the desired temperature on thermostat the fan continuously runs. I filled my propane tanks Jan 19th and I am empty already. What could be the issue

Reply:

Zenia, if the air delivered is not warm enough I'd first check for an obvious duct problem: a crimped, damaged, or disconnected supply or return duct.

If the system has never ever heated adqequately in backup mode (which would be when it faces the most demand) there may be a capacity or duct or other installation error.

If the system used to work adequately in similarly cold weather but does not now, I'd look for a burner or blower problem. E.g. a dirty air filter or dirty blower fan would reduce air flow.

If there is too much makeup outdoor air that also would cool down the delivered heat.

This does not quite sound like a thermostat problem. More diagnostic details in a more orderly presentation are in our article found by searching InspectApedia for

DIAGNOSE & FIX HEATING PROBLEMS-FURNACE

Question: thermostat for wood stove fan - Ranco

(Mar 23, 2014) karen said:
Ihave a wood stove. I want to hook up a thermostat to shut the fan off when the fire goes out or gets cold. I cannot find any information on how to do this.

Reply:

Karen, I'm not sure what fan you're trying to control, a draft inducer or a simple stand alone circulating fan, or a furnace limit switch fan controller.

If you are trying to control a simple air-circulating fan you want a thermostat that is capable of switching a 120V circuit.

Ranco and other companies make these. Before buying a device try asking Ranco for advice about using their ET-1100: Ranco, 8115 US Rte 42 North, Plain City OH 43064, (614) 873-9000 / 614-873-9554.

Question: thermostat won't turn on the AC

(May 22, 2014) daniel said:
it's summertime in houston and my thermostat is reading 40 degrees so naturally the a/c won't come on. does my thermostat need to be replaced or could it be something else?

Reply:

Daniel

Before replacing the thermostat try disconnecting it at the A/C unit and just jumping the TT terminals. A thermostat, at the end of the day, is basically an on-off switch. So that part is easy to debug.

See inspectapedia.com/aircond/Air_Conditioner_Diagnosis.php for help diagnosing an A/C that's not working

Question: need thermostat instructions

(July 2, 2014) Heather said:
We dont have instructions with it, just moved in new house with this heat pump

(Aug 18, 2014) Anonymous said:
T connection

(Oct 27, 2014) Anonymous said:
My Honeywell YCT87N1006 thermostat temperature display (correct room temp) is always 5 degrees less than my manual setting.

(Nov 15, 2014) kirby said:
my thermostat drops from 75 to 60 dregrees two to three times a night what is the solution to stop this from happening.

Question: new Honeywell thermostat is acting as bad as the one we replaced - why is temperature so off?

(Nov 16, 2014) Sam said:
Hi, we just replaced our thermostat to the Honeywell and it's doing the same thing as our last, so I don't think it's a problem. We live in a tri-level and the thermostat is in the main floor living room. I set it on 65 degrees and the top floor bedrooms are 72 degrees. Downstairs it's about 68-70 degrees all day.

On the bottom floor the room next to the room with the furnace and the furnace room are very warm. The other basement room is about 72. We have already closed and covered registers on the top floor and in the warm rooms. Why is the temperature so off? What can we do? Our bills are so high for it being set on 65.

Thanks for any help. I'm not a professional or even reasonably good at home repair.

Reply:

Sam

If a thermostat is located nowhere near the rooms whose heat it controls it may not do what you want. It's typical for heat to move upwards in a building, making upper floors warmer.

You'd need to relocate the thermostat or set it back to a lower temperature.

Not very costly and effective: install thermostatically controlled radiator valves at individual baseboards - possible or not possible depending on the piping layout of the building.

More costly but possible: ask your heating company what would be involved in making each floor into its own heating zone.

Question: trying to replace a Ritetemp 6010 with a Honeywell RTH2410B

(Jan 3, 2015) James Hunt said:

I am trying to replace a Ritetemp 6010 with a Honeywell RTH2410B. Four wires coming from wall: Red to W2, White to W, Yellow to Y, and Blue to G. (no R wire). In the new unit, I do not know where to connect the Red (w2) wire.

I am thinking it should go to the R terminal on the Honeywell which is jumpered to an Rc terminal. The actual AC unit is not used at all. (no cooling needed). If I am not mistaken, I am trying to make this new TSTAT work in a multi stage system and thus the dilemma.

Reply:

Honeywell offers wiring suggestions for almost every hook-up. Or start at THERMOSTAT WIRING HONEYWELL

Question:

(Feb 25, 2015) mr air con & ref said:
ef error code on tlc split cassette

(Mar 6, 2015) Pat said:
Just had furnace installed, going to add an ac in the spring. Installer took old thermostat off wall, he couldn't find wiring needed to add ac to thermostat. I am being told that i have to hire an electrician at my own cost to rewire both furnace and ac to thermostat. Shouldn't it be their responsibilty, wiring was ok till they started to work on the hookups.

Reply:

This is a contract question not a technical one. My OPINION is that the installation of a new furnace should include hooking up its controls.

Question: cannot move thermostat switch to COOL

(Apr 27, 2015) Jeannine Thompson (Bow Island) said:
My Carrier thermostat works fine on heat, but I can't move it to "cool"

Reply:

Jeannine

If you mean that the thermostat switch is physically stuck then you may need to replace the device.

Question: Where can I find an "old fashioned" remote controlled thermostat

(Apr 28, 2015) MIKE said: Where can I find an "old fashioned" remote controlled thermostat for my central air/heat.

I'm not interested in wifi or smart phone/computer programming therm. Just a simple on/off, hi/low blower, that's all. If you could email me at: mikepaskas@gmail.Com I would appreciate it.

7 August 2015 Anonymous said:
Thermostat that be controlled by smart phone?

Reply: some remote control heating or cooling (or both) thermostat sources

Mike,

You don't want a NEST thermostat that can be controlled from your smartphone. But you do want a thermostat that has a remote-control. From this I presume you mean a hand-held remote control device. The most common hand-held remote controlled thermostatic devices are those sold with split-system air conditioners and heat pumps, using an IR beam (or equivalent) to communicate with the wall mounted air handler.

But besides there are a number of companies selling "wireless thermostats" either alone or as part of "smart home" packages. Prices range from $50. to $200. USD and technologies include wi-fi powered systems, Z-wave, ZigBee, and Insteon thermostats. Insteon thermostats, around $150. like the Insteon 2441TH can be controlled from anywhere in your home using an RF device from distances up to about 150 feet (50 meters).

I wouldn't consider these thermostats quite "old fashioned" but they do work as you specified, using a hand-held remote controller rather than a smartphone.

Here are some remote control heating or cooling (or both) thermostat sources. Virtuallyi all of these companies offer multiple thermostat models with a wide variety of functions including remote control of the room thermostat.

• 2GIG Technologies CT100-345 Z-wave Thermostat
• Aprilaire, 8800 TOuchscreen communicating thermostat
• Bay Controls BW-WT2-W internet thermostat
• Ecobee EB-State3 Smart Wi-Fi thermostat
• Honeywell Wi-Fi "Smart" Thermostat
• Honeywell RCH9300WF500U Lyric Smart Wi-Fi Thermostat (looks remarkably like the "Nest" thermostat
• IP Thermostat with multiple ethernet ports permits web-control of the thermostats in your home
• Insteon, 16542 Millikan Ave., Irvine, CA 92606, 800-762-7845, www.insteon.com
• Jackson Systems WCT-32 Wireless Comfrot Thermostat
• LockState Connect LS-90i Wi-Fi thermostat
• Leviton Security & Automation RT200-W Omnistat2 Multistate thermostat connects to home automation systems
• SCI USA CEM24 Super Telephone Thermostat, remote control by telephone
• Venstar ACC0454 Skyport Wi-Fi thermostat
• Z-Wave Residential Control Systems 001-01773 TZ45 Communicating Thermostat

Note: These and other remote control room thermostats are widely sold online both at generic retailers such as Amazon and Grainger and also at specialty retailers such as at smarthome.com

Anon:

The NEST thermostats can be controlled from your smartphone.

Question: how to wire up a thermostat for separate heating and cooling functions

(June 3, 2015) Anonymous said:
Have a programmable thermostat (TH). What to add a second, to separate the heating and cooling functions.

First TH switch, would be set to “Heat” the second to “Cool”. Both would be set to the same temperature. If it’s COLD, the “Heat” turns on, and if it’s HOT, the “Cool” turns on, but not both at the same time.

On the first TH, would remove the “Y” connection and place it on the “Y” connection of the second.

Bridge a ground wire between both.

Are there other consideration, logic/delay circuits, needed in order for this option to work?

Any schematic/help would be helpful.
Thank You…

Reply:

I'm a but unclear on your question, Anon, but indeed at THERMOSTAT WIRE CONNECTIONS you will find extensive wiring diagrams and instructions for hooking up most types of room thermostats.

Or you can give us your thermostat model and brand and we can help dig up that data.

Most room thermostats can control both heating and cooling equipment but you'll need to first check that your thermostat wiring bundle includes enough separate wires to connect to the different thermostat control terminals on that end and to the heating or cooling devices on the other end.

Question: replaced thermostat, now both old and new units don't work

(June 18, 2015) Ray said:
Replaced old thermostat with new one but would not work so I put old one back and now it will not work. A/C will not come on at all.

Reply:

Ray

Check for loose, broken, shorted thermostat wires.

Check for a blown fuse

Check for a blown thermostat transformer

Question: thermostat display won't stay on

(June 18, 2015) Anonymous said:
i am trying to replace an old thermostat in a small old condo that has hot water baseboard heating. When I installed the new two wired unit, the display showed for a few seconds and then disappeared.

When I took the cover off, the display reappeared and then disappeared When I pushed the up or down button temperature button. Its just a simple 220 unit, no battery. What is happening? Thanks

Reply:

Sounds like a wiring error, wrong thermostat type, or a defective unit.

Question: which way to turn the dial on a window AC unit?

(July 14, 2015) Thor said:
This might be a stupid question but i have a window unit ac and on the thermostat dial it goes 1-9. Its old so when i go from 1 to 9 or 9 to 1 there is a noise change but the air feels the same, my question is, is 1 the coldest setting or is 9?
flag like

Reply:

Thor,

Thanks for asking, there are no stupid questions.

Typically the highest number is the coldest setting on a window A/C unit temperature control. You can confirm this by noting that (with a working system) if the unit is running and you set the dial to a lower number the unit will turn off (the control assumes you're saying it's cool enough now).

The noise change when you turn up to a cooler setting is probably the compressor motor turning on.

But if no cool air ever comes out of the system (give it five minutes to get going and cool down) then there is a problem, perhaps lost refrigerant.

Question: Honeywell RTH2300 thermostat not responding properly to room temperature

12 August 2015 Bryan said:
Office environment with a HONEYWELL RTH2300 thermostat . .

. in Cool mode Fan On and set to 75F Hold . . . cooling does not click on until 77F reached on display temp . . .

and does not click off until 73F reached on display temp . . . I would think cooling should click on when above 75F . .

. ie at 76F . . . and click off when below 75F . . . ie at 74F . . . is this operating within standard tolerance? . . .

is the thermostat defective? . . . is there any means to rectify to hold at 75F?

Right now there is a 4 degree variance which at 77F is slightly too warm and at 73F is slightly too cool . . .

would be better clicking on at 76F and off at 74F.

Thought about changing the batteries but don’t think that should have any effect as cooling is clicking on and off OK and display reading OK just at higher and lower temps than the setting.
Any comments or suggestions to rectify would be greatly appreciated.
Thanks,

Reply: check for dirt, dust, or drafts before replacing a non-responsive thermostat

Good question, Bryan. I like the Honeywell RTH 2300 thermostat series an have installed a number of them without having the trouble you describe.

I'd expect the thermostat to respond just as you do. And I'm doubtful that batteries are the problem.

1. FIRST: inspect the thermostat closely to be sure that no clod of dust or crud is blocking the little thermistor that senses temperature.
2. SECOND: check that the thermostat is not being confused by external conditions such as location on a wall that exposes the thermostat to hotter or cooler temperatures than the actual room temp.
   
   A subtle example can be a convection current running through an uninsulated interior wall cavity that is blowing cool air into the thermostat from its back-side through the wiring opening in the wall. This is probably not your problem since if the thermostat were being thrown off by sunlight, wall mounting location, or drafts, I'd expect its room temperature to reflect that influence.
   
   You'd see instead a gap between the room temperature shown by the thermostat's indicator and an independent measurement of room temperature say in the middle of the room.

A programmed setting can also confuse us about how the thermostat should be responding if a thermostat is running under a program whose settings are not what we thought.

But if you've got the thermostat in HOLD mode then it ought to respond to temperature changes around the hold temperature setting. Double check that you see the word "HOLD" in the display.

This Honeywell RTH2300 thermostat has some self-diagnosing circuitry which I summarize:

• It will display low battery ("Lo Batt") for 60 days before the battery is dead.
• HI: the ambient temp is above 120F
• LO: the ambient temp is below 32F - these are the operating limits of the device
• E1 or E2 = bad sensor, replace the thermostat

I'd give the company a call to ask about the response you're experiencing:

Call Honeywell Customer Care toll-free at 1-800-468-1502 or see the company's consumer website at DIYthermostats.honeywell.com.

See 4-Wire Honeywell RTH2300 Programmable Thermostat Wiring diagrams for help with wiring this thermostat.

We also include this copy of the Honeywell RTH2300/RTH221 Series Programmable Thermostat Owners Manual [PDF]

Also see THERMOSTAT CALIBRATION where we discuss the accuracy and calibration of room thermostats.

If your heating system is not working at all, start at HEAT WON'T TURN ON.

Question: thermostat display is blank

(Oct 10, 2015) Bill Adkins said:
I have a Trane heat pump with a Honeywell electronic thermostat. We went to reset the thermostat and it was blank. Needless to say the A/C is not working now. I feel like it is probably something simple but I really have no idea.

Reply:

Bill a blank thermostat display usually means that the unit has no power - either power is off to the equipment that the thermostat controls (and from which it is powered) or for some units that rely only on batteries the batteries are probably dead. Keep me posted.

Also see WHITE RODGERS CONTROLS & MANUALS

Question: thermostat not doing what it should to the blower fan

(Nov 27, 2015) rick said:
I know his may be an age old problem but I can't find a post describing my exact problem.
equipment - New Lennox Heat Pump unit.
Thermostat - White Rodgers heat pump thermostat (6 months old)

Problem example: Set point set at 69 degrees. Unit will come on normally with fan on, heat strips on and heat pump compressor energizes.

When inside heat reaches 69 degrees, thermostat clicks and heat strips turn off and outside compressor de-energizes but - fan continues to run and will run all night if temp stay at 69 or below. If temp falls below 69 set point, heat strips will again come on and compressor with energize again.
Cycle will continue with the same result,,,,, fan will not shut off.

** If I manually raise the temperature myself to 70 degrees, the fan will turn off. *** Process will repeat itself no matter what temp I set it at.

Fan is in Auto setting, Control is in Heat setting, not emergency setting.

You guys have any idea what my problem might be? I would suspect the thermostat but I had the same problem with the previously installed unit and another thermostat. Bad wiring / shorting out? If wiring were shorted, fan wouldn't shut off when I raise the temp manually.

I tried changing the batteries in thermostat as one guy suggested. Put in new thermostat? I could try that again, but hate to go through the expense and I have two of the same thermostats (upstairs and downstairs). Have to teach spouse to use yet another thermostat. Not what I really want to do!

ANY ideas would be helpful! Thanks!

Reply:

Rick:

Typically the blower fan in an air handler is controlled by a separate fan limit switch. The fan is designed to continue to run a bit past the point at which the thermostat stops calling for heat - this is both to extract the remaining heat from the heat exchanger for energy efficiency and also to avoid damaging a heat exchanger by stopping the air flow across it when it is still quite hot.

Once the heat exchanger has cooled off the limit switch will turn off the blower.

Search InspectApedia for FAN LIMIT SWITCH to read about how to inspect and test this switch.

Question: no heat, blamed on thermostat

(Nov 22, 2015) Cassandra said:
I'm in a rental that's an old building made into apartments. Our boiler is not putting out heat. We had a service person in and I told them the wiring on the thermostat was the issue. They replaced the thermostat, but not the wiring.

Heat worked for a bit, then has stopped. Fiddled with wiring, but it won't ignite.

The unit snaps, and sounds like it's going to come on, but then it shuts itself off. Something is telling it to turn off, even though it's freezing in here. Could this be a pump issue or thermostat/wiring problem. serviceman checked to make sure the air hose was not backed up with leaves.

A bit confused and cold at this point. Have to wait until morning to get a service person out...

Reply:

Cassandra

Let's separate two situations:

If the thermostat does not call for heat - say because a wire is loose or broken - then turning it up (or when the temperature drops) the boiler will not respond nor will the hot water circulating pump(s).

If the thermostat is working and calls for heat then typically it turns on a circulator pump and water begins to circulate through rads or baseboards. Cold water returning to the boiler drops the boiler temperature and its aquastat turns on the boiler.

If the boiler never turns on then there is a control problem OR a maintenance and repair problem that may have left the burner off on safety-reset.

...

Continue reading at THERMOSTAT DIAGNOSTIC GUIDE or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see THERMOSTATS, DIAGNOSTIC FAQs-2 - more-recent thermostat troubleshooting questions and answers

Or see these

Recommended Articles

• THERMOSTATS, HEATING / COOLING - home
• THERMOSTAT WON'T TURN OFF
• THERMOSTAT WON'T TURN ON
• THERMOSTATS, HEATING / COOLING
  • ROUND WALL THERMOSTATS & how they are set
  • RECTANGULAR WALL THERMOSTATS & how they are set
  • PROGRAMMABLE, DIGITAL THERMOSTATS & How They are Set
  • NEST LEARNING THERMOSTATS
  • RADIATOR & BASEBOARD THERMOSTATS, Automatic - TRVs
  • REMOTE CONTROL ROOM THERMOSTATS
  • STEAM HEAT ROOM THERMOSTATS
  • THERMOSTAT TEMPERATURE SENSORS
• THERMOSTAT SETTING INSTRUCTIONS - Separate article - How to Set the Thermostat
• THERMOSTAT OPERATION - how digital thermostats & their displays work
• THERMOSTAT SETBACK ADVICE
• THERMOSTAT TROUBLESHOOTING - Separate article: What to check if a thermostat is just not working
  • HEAT ANTICIPATOR ADJUSTMENT
  • HEAT ANTICIPATOR ADJUSTMENT - T87
  • THERMOSTAT ERROR CODES - How to Translate the error codes on digital thermostats
• THERMOSTAT WIRE CONNECTIONS - how to wire up all types and brands of heating & cooling thermostats- how to wire up all types and brands of heating & cooling thermostats

Suggested citation for this web page

THERMOSTATS, DIAGNOSTIC FAQs at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to HVAC THERMOSTATS

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