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Photograph of  a modern oil-fired heating boilerNo Heat Diagnosis
for Oil or Gas Fired Hot Water Heating Boilers

  • POST a QUESTION or COMMENT about how to fix a heating boiler that is not working - how to diagnose the loss of heat in a building when the heat source is an oil or gas fired boiler

Heating boiler problem diagnosis and repair guide - no heat or loss of heat calls:

Here we explain how to recognize & diagnose no-heat problems with residential heating boilers, including loss of heat, heating boiler noises, leaks, odors, or smoke, and high heating costs.

This article explains the diagnosis and correction of no heat conditions for water or hydronic or hot water or radiator or baseboard hot water heating systems.

We give help in troubleshooting heating systems using LP gas (propane) or natural gas. How to inspect & repair central hot water heating boilers - hydronic heating. Baseboard, radiator, convector heat inspection, defects, repairs.

This website answers questions about all types of heating systems, advising on troubleshooting, inspection, diagnosis, and repairs. We describe how to inspect, troubleshoot and repair heating and air conditioning systems to inform home owners, buyers, and home inspectors of common heating system defects.

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

How to Diagnose a "no heat" problem: steps the occupant or owner can take before calling repair

Heaing system emergency switch (C) Daniel FriedmanHot Water Heating System: Once you confirm that your heat is made by hot water (a heating boiler) you might want to review hot water or "hydronic" heating systems

at BOILER COMPONENTS & PARTS
and

at BOILER OPERATING STEPS where we describe the parts and operating sequence of hot water heating systems.

Note: some hybrid or mixed heating systems combine both hot water and hot air to heat a building, such as water to air systems which use a heating boiler (oil, gas, or electric) to heat water which circulates through (and inside of) a heat exchanger (that looks like a car radiator) - described

at HEATING SYSTEM TYPES.

If your heat is by forced warm air, it's not a boiler and you're on the wrong page: instead please

see NO HEAT - FURNACE

If you don't know whether your heat is provided by a furnace (hot air) or boiler (hot water), or whether your fuel is oil, gas, or electric, and whether your heat is hot water, steam, or warm air,

see HEATING SYSTEM TYPES.

Types of Defects and Problems with Hot Water Heating Boilers - Hydronic Heating Systems, Loss of Heat, Noises, Leaks

Rusty, leaky, old and inefficient boiler in a wet crawl space gets far too little service (C) Daniel Friedman at InspectApedia.comWhat sort of defects should you look for when inspecting a heating system?

How to Diagnose Loss of Heat With Oil-Fired or Gas-Fired Hot Water Heating Systems - hydronic heating system troubleshooting

If the heating boiler oil burner is not turning on at all check the causes listed on this page. We'll take you through photo-illustrated step by step things to do when you have no heat and you need to determine what's wrong. First let's review these simple "no heat" concepts .

NO HEAT: BURNER OFF, SAFETY NOT TRIPPED: - Oil or gas burner has stopped, no safety switch is tripped

1. Is the thermostat calling for heat?

 check that the room thermostat setting is at least 5 degrees above the actual room temperature.

See THERMOSTATS.

2. No electrical power:

check that all of the switches that power on the oil or gas burner are in the "on" position. Check heating circuit fuses & circuit breakers, not just the wall switch. We discuss this in detail just below.

3. Is there fuel in the oil tank or LP gas tank? 

Check your oil tank or LP gas tank tank gauge.

Out of heating oil?

 If the marker in your oil tank gauge reads 1/8 full or less, or is at the bottom or out of sight you are probably out of oil. If your oil tank is buried, and if you do not have an indoor (remote) fuel level gauge, the oil level is checked in the tank by removing the tank filler pipe cap and using a long (clean) stick (or in emergency a clean string and weight) to measure the depth of heating oil in the tank.

Remember that a problem with the oil piping, oil filter, or fuel unit can also cause no oil to be delivered to the oil burner even if plenty of oil is in the tank.

See OIL BURNER FUEL UNIT for some helpful diagnostics
and

also OIL & GAS PIPING.

Out of LP liquid propane gas?

Check the gauge on your propane tank. If the reading is 10% or less you are out of fuel.

If your boiler is fueled by piped-in natural gas from a utility company, check that the company hasn't turned off your gas supply at the gas meter - something that might happen if you didn't pay a gas bill or if the gas company thought your building's gas system was unsafe.

4. Electric motor problem at the burner or blower fan:

Check that an electric motor (for the oil burner, gas burner, or blower assembly) reset switch may have tripped. See our notes above about electric motors, and

See RESET SWITCH, ELECTRIC MOTOR.

5. Aquastat or cad cell control or relay trouble:

if you hear or have ever heard buzzing from any heating system control that includes a relay switch, watch out for a control cover that is in contact with a relay switch in the unit.

If the cover is lightly touching the relay switch the control may simply buzz when the relay is trying to move.

But a too-tight control cover can also prevent a relay from operating, leading to loss of heat. Simply pulling off the cover to let the relay move freely can immediately discover and "fix" this problem.

Details and illustrations including diagnosing buzzing relays are

at HEATING SYSTEM NOISE DIAGNOSIS.

NO HEAT: BURNER HAS TURNED OFF ON SAFETY: Oil or gas burner has stopped, the safety switch is "off" or "tripped"

If you are not sure how to find and check the safety control reset buttons on your heating system, we describe these controls in more detail just a bit further on in this article.

The burner on your heating boiler, furnace, or water heater has shut down, if a red "reset button" has popped up on the burner primary control or on an electric motor that operates the system. This condition is called "Safety Off".

Watch out:  Before re-setting the safety switch or button, it's a good idea check the following five common causes of loss of heat leading to a Safety Off condition. Photos and details follow these short paragraphs.

How to press the heating system reset button:

 If you do not see anything wrong, you can try re-setting the heating system: press and hold the red reset button down for 3 seconds and release it. If the heating system has electricity it will try to re-start.

Watch out:  If the system does not keep running smoothly don't keep pressing the reset button - that could flood the combustion chamber with unburned fuel, causing a dangerous puff-back.

Just press the reset button once.  If the heating system starts and runs ok, you still should request a service call, but you can have heat while you're waiting.

1. Heating fuel failures -

out of oil in the oil tank, clogged oil filter, clogged oil nozzle, oil line has been bent, crimped, clogged, clogged oil pump strainer (fuel unit strainer), or inability of the fuel unit to pump oil (broken motor shaft, missing internal bypass plug on a two line oil tank system, an air leak in the oil inlet line, or a leaky foot valve in the oil tank causing loss of oil prime). if the oil tank is outdoors in freezing weather the oil in the tank or in an oil line may have become waxy or jelled.

2. Oil burner motor failure: t

the electric motor that runs the oil burner may itself have gone off on reset. Some causes of electric motor failure: one pipe oil system with the bypass plug installed in the fuel unit (oil pump) causing excessive pressure and stalling the motor; centrifugal motor switch sticking (try banging on the motor once); motor condenser burned out; motor stator or internal windings burned or shorted; motor bearing failure.

Try re-starting the motor -

see RESET SWITCH, ELECTRIC MOTOR

3. Oil burner ignition failure

the oil burner's ignition transformer terminals are loose; the electrodes on the burner nozzle are dirty or not set to the proper gap; the oil is contaminated and is hard to ignite; the ignition transformer has become weak or has burned out (look for tar oozing out of the ignition transformer container); the oil burner nozzle is clogged preventing oil from contacting the ignition spark arc; the ignition electrode(s) are grounded on the air tube of the burner;

4. Faulty heating system control operation

the safety sensor that checks that a good oil burner flame has been established is not working; a stack relay spring or cad cell eye may be dirty with soot; the stack temperature may be too low for the stack relay (boiler is under-fired); the oil burner has been cycling on and off to frequently (a problem with the thermostat).

Tip: Look for loose electrical connections

before deciding that a control or switch has failed, confirm that the system has electrical power, all switches are on, and that a wiring connection has not come loose.

On a recent no-heat call we were embarrassed to learn from Bob, the service tech, that the problem was most likely that somebody (who me?) may have accidentally knocked loose the electrical connector at the oil delay valve (aka "quick stop valve").

The connector may still appear to be in place but may have been pushed slightly back or askew. The result is that on a call for heat the oil burner motor will run but the burner will never ignite. Details about loose connector diagnosis & cures for the quick stop valve or oil delay valve or the PD Timer are

at OIL LINE QUICK STOP VALVES.

Other common loose electrical connections might be at wiring to any heating control or at the oil burner itself.

5. Irregular stack temperatures

in the flue can cause oil burner draft and temperature or control problems. Downdrafts (missing chimney cap), insufficient draft due to chimney problems, or fluctuating oil burner flame may be at fault. Also

see CHIMNEY INSPECTION DIAGNOSIS REPAIR.

-- some of this material is paraphrased from Audel.

Oil Burner Runs - Problems

Oil Burner Operating Problems: Oil or Gas Burner rough, noisy, smoky, smelly

The heating burner operates but not properly.

See OIL BURNER NOISE SMOKE ODORS

Next let's check each cause of no heat in detail; if your system uses warm air heat instead of water or steam, review the check-items just below before going

to HEATING LOSS DIAGNOSIS-FURNACES.

SAFETY WARNING: If a heating system oil burner has been deliberately "shut down" and you don't know when or by whom this step was taken, beware of turning the heating system back on without an inspection and safety check by an expert technician.

Heaing system emergency switch (C) Daniel Friedman
  • Electrical power to the heating boiler 

    or oil burner is OFF: check the circuit breaker or fuse supplying power to the unit; check the service switch at the furnace or air handler, and if the system is air conditioning or a heat pump, check the service switch outside at the compressor/condenser unit to be sure it is "on".

    Make sure that electrical power is on for all of the heating system components. Check local switches at the boiler, wall mounted boiler switches at the stairwell down to the basement or utility room or in other areas, and check the circuit breakers or fuses in the electrical panel.

Is the heating boiler turned on? Is there electric power to all of the heating system components such as an oil burner at the boiler and power to the circulator pumps?

Hidden heating system On-Off switch was flipped off leading to a NO-Heat service call (C) Daniel Friedman at InspectApedia.com

Watch out: as we illustrate above and below, there may be more than one heating boiler or furnace power On-Off switch. Often there is a service switch right at the heater, and another at the top of the basement stairway or elsewhere in the living space.

The upstairs heater on-off switch is there so that in an emergency the building occupants don't have to go down into a basement (or crawl space or other hard-to-access area) to turn off the heat.

The heating system On-Off switch shown here was "hidden" in a closet in an older New York Home. At one time the door shown almost certainly led to a stairway down to a basement under the home - the location of the heating boiler.

Later renovations eliminated the stairs to the basement, leaving only an outdoor basement entry stairs. But the boiler on-off switch remained.

Hidden heating system On-Off switch was flipped off leading to a NO-Heat service call (C) Daniel Friedman at InspectApedia.com

New homeowners didn't know what this red switch did, and one of them, thinking it "did nothing" thought it would be safer to turn the switch to its "OFF" position, so she did so.

Later when the weather turned cold the homeowners discovered that they had no heat, called their service technician for repair, and it was the technician who found this service switch and turned it back to "ON" so that heat could be restored.

Hidden heating system On-Off switch was flipped off leading to a NO-Heat service call (C) Daniel Friedman at InspectApedia.com


Photograph of an oil fired heater stack relay

Where are all the heating system reset buttons? If you are looking for the main reset button on heating equipment you'll want to

see:

AQUASTAT CONTROL FUNCTIONS

CAD CELL RELAY SWITCH (hot water boilers and some water heaters),

STACK RELAY SWITCH On older oil fired boilers and furnaces,

FLUE GAS SPILL SWITCH TRIPPING & RESET (gas fired equipment),

and

LOW WATER CUTOFF CONTROLS On steam heating systems.

At ELECTRIC MOTOR OVERLOAD RESET SWITCH we discuss the thermal overload switch and reset button that is found on many electric motors including those operating air conditioning fans, heating system oil burners, and furnace blowers and motors.

A Stack relay switch may be installed on the flue vent connector and may be in the "safety - off" position. To identify and reset this control see STACK RELAY SWITCH. Stack relays are found on older oil fired furnaces and boilers.

Still no heat? Once you have assured that you have heating fuel and that electrical power is turned on to the heating unit, if you still don't have heat check these controls:

Heating Boiler Runs but No Heat is Delivered

How to Diagnose Soot or Noises during Heating System & Oil Burner Operation

For full details of this topic be sure to

see OIL BURNER NOISE SMOKE ODORS.

How to Evaluate Heating Boiler Leaks & Corrosion

For full details of this topic see BOILER LEAKS CORROSION STAINS

When observing evidence of leaks on a heating boiler, keep these points in mind:

A Catalog of Common Heating System Leak Points - Where to Watch for Heating System Leaks

How to Recognize & Diagnose Inadequate Combustion Air for Oil-Fired Heating Systems

Heating system combustion air sketch Carson Dunlop Associates

For full details of this topic

see INADEQUATE COMBUSTION AIR

Lack of adequate combustion air

can result in improper system operation, sooting, increased heating cost, damage to oil burner components (back pressure heat can destroy an ignition transformer), higher and more frequent heating service costs, loss of heat, noises, smoke, and potentially, the production of carbon monoxide or other flue or combustion gases which escape into the building - potentially dangerous

Watch Out:  The sketch shown here, courtesy of Carson Dunlop Associates, explains how dangerous furnace back-drafting can occur when there is insufficient combustion air.

These conditions can not only release flue gases into the occupied space, but they are likely to cause the production of potentially fatal carbon monoxide.

We've seen heating equipment that seemed to work just fine during its adjustment because the service technician was working with the door to the furnace or boiler room open. But when she left the system and closed the furnace room door, suddenly there was insufficient combustion air.

Also see Unsafe Air Conditioning or Heating Duct Openings which describes the risks of reduced combustion air on hot air heating systems when certain return air duct defects are present,

and also see CARBON MONOXIDE - CO

and CHIMNEY INSPECTION DIAGNOSIS REPAIR

A Guide to Heating Equipment Malfunctions & Their Implications

Examples of Heating System Defects with Important Implications

 

 

Reader Q&A - also see the FAQs series linked below

On 2020-09-23 - by (mod) - baseboards don't get hot

Tony

It's possible that the settings on your aqua stat are incorrect.

In the ARTICLE INDEX you will see an AQUASTAT SETTINGS article on what the proper settings are.

On 2020-09-23 by Tony

I had a Navida Tankless water heater installed for hot water only, the big water tank was removed from my oil burning system for the baseboard heaters,

now my baseboard heaters are not getting hot, the boiler is at 180 and the hot water seams to be going out back the baseboards are not hot, and the return lines are cold,

Was the hot water tank needed to still run the baseboard heaters ?

On 2020-05-15 - by (mod) -

Jerry,

That smoky flame tells us the oil burner is out if adjustment and so locking out is normal.

On 2020-05-14 by JERRY

boiler will purge , ignition is immediate after purge ,fires thru trial period very smoky, goes to hard lockout after trial period Has new nozzle ,cleaned boiler, new cad cell , cleaned screen on pump.air settings the same as it has always run
any ideas on what is causing failure

On 2020-02-21 2 - by (mod) -

Also can you post a photo of your boiler and another of its data tag (one image per comment) ? I don't have a Hydrotherm HI B 85/50 boiler manual nor can I find that exact boiler name.

I'm looking into the question in more-detail John and will report back.

If you don't have it, the manual for your aquastat is at

i HONEYWELL L4080B AQUASTAT MANUAL [PDF]

that also covers the HONEYWELL L8080A AQUASTAT MANUAL [PDF]


Honeywell's own website provides no literature for the L4080 / L8080 nor does the company list a replacement, though the L4080 - series and L8080- series aquastats are certainly listed as a available by many supply houses.

Also the Honeywell L7224U might suit.

But to the point of your question, I don't see that the L4080 has within itself specific provision for dual fire-level boilers.

The L4040B aquastat is a simple high limit aquastat controller with a single adjustable set-point using an internal dial inside the aquastat.

On 2020-02-21 by John

How do I set dial and locking arm on Honeywell L4080B 1212 Aquastat? This is a Two stage HI B 85/50 Hydrotherm boiler.
Boiler will not go from hi fire to low fire after return water reaches its maximum setting.
Please advise

On 2020-01-22 - by (mod) -

Mike

Is the boiler's burner shutting off because it's reaching the hi limit, because the thermostat is satisfied, or because of an operating problem?

About the line that doesn't get hot, in the ARTICLE INDEX above see AIRBOUND HEATING SYSTEM for troubleshooting and repair

On 2020-01-21 by Mike

There’s 2 pipes coming out of burner one gets hot the other staying cold and burner runs for a few minutes and shuts off.

On 2020-01-08 - by (mod) -

Johnny you posted this question and we replied at

BOILER OPERATING STEPS

That sequence uses an oil burner as an example but a gas fired heating boiler would use all of the same steps except that it's a gas valve that opens and gas burner that ignites (by pilot or by electronic ignition) rather than oil burner igniting by a transformer electrode.


Please help me out: with thousands of readers and reader questions, avoid doubling our work in responding by posting just once.

On 2020-01-08 by Johnny

Can anyone post a flow chart on a gas hot water boiler as to how when the thermostat calls for heat the sequence that follows ( the thermostat closes and the power goes to ?
and so on
Thank you for your help
bossjohn@optonline.net

On 2019-12-19 b (mod) - Weil-mclain CG 11 hot water boiler gas usage rate

Gas fired hydronic heating boiler Weil McLaain CG-11 (C) InspectApedia.com JimmyJimmy

I can't guess how much LP gas use is normal for your home because the amount of fuel needed and heat output needed to warm a home varies significantly by the home's rate of heat loss (how well a home is insulated, how much air leakage there is, how much glass there is, how much opening and closing of windows and doors occurs, etc).

But there are some sanity checks that one can make.

1. Look at the heating boiler's data tag where you'll see the input BTUh consumption rate of your boiler.

At GAS BTUH, CUBIC FEET & ENERGY we give all of the ways to convert between cubic feet or other measures of LPG and btus. You can thus start by seeing the rate per hour (of "on" time) at which your boiler consumes fuel.

You'll need to watch or measure or count hours-on for your boiler.

2. Have your heating service tech be sure that the boiler is properly tuned and adjusted. If your boiler's HI limit is set to 180degF that does NOT mean that the baseboard pipes will ever see that temperature; there is heat loss enroute;

However your tech might agree to push up the HI to 190 or closer to 200F (not above that or the TPR valve will open); the thermal conductivity of baseboard is exponentially greater at higher temperatures so you'll see a bit more efficient heat transfer into the occupied space.

3. InspectApedia offers a number of articles on cutting heating cost by finding where the waste or leaks are.

Two articles I like are

ENERGY SAVINGS PRIORITIES

and

HEATING COST SAVINGS METHODS


3. There are plenty of additional heat savings articles recommended at those pages I just cited.

On 2019-12-19 by jimmy45

Thank you for taking the time
Our home is a late 60's pre-built with 1150 square feet. We have a Weil-mclain CG 11 hot water boiler, Taco sentry zone valve on the supply side, and I think the issue is with the zone valve.

We use 10% LP on a 500 gal. tank a week. When the thermostat calls, the zone valve closes, the boiler fires, as does the circulator.

The baseboards get warm to the touch, but not 180 degree hot. Once the heat is reached, the boiler stops as does the circulator, and the zone valve opens. We have our thermo set at 65, it turns out around 63 degrees, and shuts of around 66. It takes close to an hour to raise 3 degrees.

Is this much LP normal?
How has no damage occurred with the circulator running and the zone valve closed?

Thank you for your time

...

Continue reading at BOILER OPERATING PROBLEMS or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see BOILER REPAIR DIAGNOSTIC FAQs - questions & answers posted originally at this page.

Or see this

Article Series Contents

Suggested citation for this web page

DIAGNOSE & FIX HEATING PROBLEMS-BOILER 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 HEATING BOILERS

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