Question? Just ask us!
Free Encyclopedia of Building & Environmental Inspection, Testing, Diagnosis, Repair
InspectAPedia ® Home
AIR CONDITIONING & HEAT PUMP SYSTEMS
BACKDRAFTING HEATING EQUIPMENT
BACKUP HEAT for HEAT PUMPS
BANGING HEATING PIPES RADIATORS
BLOWER FAN OPERATION & TESTING
BOOKSTORE - InspectAPedia
BTU USAGE MONITORS
CARBON MONOXIDE - CO
CIRCULATOR PUMPS & RELAYS
DIAGNOSTIC GUIDES A/C / HEAT PUMP
DIAGNOSE & FIX HEATING PROBLEMS-BOILER
DIAGNOSE & FIX HEATING PROBLEMS-FURNACE
DIRECT VENTS / SIDE WALL VENTS
DRAFT REGULATORS, DAMPERS, BOOSTERS
DUCT SYSTEM & DUCT DEFECTS
ELECTRIC HEAT, DIAGNOSIS, REPAIR
ELECTRIC MOTOR DIAGNOSTIC GUIDE
FAN, AIR HANDLER BLOWER UNIT
FLOODED HEATING EQUIPMENT REPAIR
FLUE SIZE SPECIFICATIONS
GAS BURNER Flame & Noise Defects
GAS PIPING, VALVES, CONTROLS
GEOTHERMAL HEATING SYSTEMS
HEAT PUMPS, DIAGNOSIS, REPAIR
HEATING COST SAVINGS METHODS
HEATING OIL PIPING TROUBLES
HEATING OIL TANKS
HEATING SYSTEM NOISES
HEATING SYSTEM TYPES
LP & Natural Gas Safety Hazards
MANUALS & PARTS GUIDES - HVAC
MIXING / ANTI-SCALD VALVES
MOTOR OVERLOAD RESET SWITCH
NOISE, HEATING SYSTEMS
ODORS FROM HEATING SYSTEMS
OIL FILTERS on HEATING EQUIPMENT
OIL FILL PIPE LEAKS
OIL SPILL CLEANUP / PREVENTION
PLASTIC HEATER VENT
PUFFBACKS, OIL BURNER
RELIEF VALVE LEAKS
Reset Switch - Heater Primary Control
RESET SWITCH - ELECTRIC MOTOR
Reset Switch - Stack Relays
SAFETY, HEATING INSPECTION
SAFETY RECALLS, Chimneys, Vents, Heaters
SOLAR HEATING SYSTEM DESIGNS
SOOT on OIL FIRED HEATING EQUIPMENT
STEAM HEATING SYSTEMS
THERMOSTATS, HEATING / COOLING
VIDEO GUIDES: Heating System Videos
WINTERIZE A BUILDING
WOOD, COAL STOVES & FIREPLACES
WOOD STOVE SAFETY
Zone valves on hot water heating systems: what is a zone valve, how do they work.How do I choose & install a zone valve, how do I wire up a zone valve, and how do I troubleshoot, repair or replace a zone valve?
This website answers most questions about Heating System Boiler Controls on central heating systems to aid in troubleshooting, inspection, diagnosis, and repairs. The photo above shows a a bank of six zone valves controlling heat distribution in a large home.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
Our photo at left shows a Honeywell (TM) zone valve installation.
Heating water piping in a building, particularly where hot water baseboard heat is used, may be divided into separate heating zones (different floors, or different areas on a single floor) to permit more detailed control of heat distribution in a building.
The control of heating water through these different heating zones may be accomplished by use of zone valves (one per heating zone or area or "loop" of heating piping) which in turn are connected to individual thermostats.
When the thermostat calls for heat in a particular building area, the thermostat switch causes the zone valve to open, to permit hot water to flow through that zone.
Other brands of zone valves such as those made by Flair (TM) (problem prone), and White Rodgers work similarly but their wiring may be slightly different. Wiring details for the yellow Flair Zone-A-Trol valve shown above are given at ZONE VALVE WIRING
In all cases, when the zone valve is fully open, an "end switch" inside the valve tells the heating system's circulator to begin operating, causing hot water to flow through the zone.
Typically heating systems using zone valves will have two or more zone valves (usually but not always located close to the heating boiler) and a single circulator pump (usually located on the return end of the hot water piping close to the heating boiler).
But if you see a zone valve with the cover off (photo at left) that may be a clue that the valve has been having problems with jamming or sticking - someone left the cover off to try to keep the valve a little cooler.
Good installation details install a zone valve on the return side of the heating piping loop where it will be exposed to lower and thus less stressful temperatures.
While going through the detailed sequence in the operation of the heating boiler, watch for and inspect the condition of the heating boiler controls and safety devices (as required by ASHI 9.1.A.3 automatic safety controls).
A typical design will include a thermostat on the water heater that will cause hot water from a physically separate heating boiler to circulate through the heating coil located in the bottom of the indirect-fired water heater.
A separate loop of piping conducts water from a nearby heating boiler, through the coil in the bottom of the indirect fired water heater tank (thus transferring heat to water in the water heater tank), and back to the heating boiler.
Sketch (left) courtesy of Carson Dunlop Associates.
The water temperature inside the indirect fired water heater tank is sensed by a thermostatic control that causes the hot water tank's contents to be re-heated as needed, typically by turning on a circulator pump that moves hot water from the separate heating boiler through the coil in the bottom of the water heater.
While typical indirect water heaters use a heating loop encompassing a circulator pump and check valve, some systems may use a zone valve in this piping loop that first opens to let hot water flow though the piping loop (boiler to water heater coil and back to boiler), and second, when the valve has opened, it turns on a circulator pump to cause water movement.
This arrangement (or a simple check valve) prevents water in the hot water tank from being heated by the boiler when it is not needed (circulating by convection, for example).
See Indirect-fired Water Heaters for details.
Green link shows where you are in this article series.
Frequently Asked Questions (FAQs) About Zone Valve Controls for hot water heating systems
Question: After adding a third zone valve one of my other heating zones stopped working
I have a two zone heating system with two thermostats and one circulator. I recently added a third zone for my basement. I have not wired in the zone valve and T-stat yet for the new zone. Since adding my third (non active) zone my 2nd floor zone has stopped working.
If I manually open the valve then when the circulator starts to heat the first floor it pushes water around the second floor as well. I have tried testing voltages across terminals 1 and 2 and 2 and 3 but I get no readings either on the bad zone or the good one. I would have expected to see 24V on at least the working zone but I don't. Why is that ?
I have checked the connections to the thermostats and transformer and all seem secure. Also I noticed that my transformer doesn't appear to be sending out power - do I need to be there when something else tells it to send out power or is it constant. If it's constant and I have no power then how is my system working at all ?
It wound up being an airlock. I just kept purging and purging and eventually got it.
Will, when you added the new zone valve to the heating system piping, the operation of cutting the heat distribution piping and soldering in the new zone valve could have introduced air into the heating system. If you didn't bleed that air out or provide an automatic air bleeder in a location that would do that for you, your system could be airbound. To check for, diagnose, and fix that problem, see AIRBOUND HEAT SYSTEM REPAIRS if you need to address this problem again.
Question: zone valve makes clicking noise when it is fully open and gear motor continues to run
Eric zone valve vt2343g13a02a works good but when in the open position it keeps clicking like the gear motor continues to run and the gear is clicking on the last tooth of the actuator or something???? - Ken 11/23/11
Ken a zone valve that keeps clicking suggests to me that either
the zone valve motor gears have become stripped or
the valve assembly is jammed and is not opening fully - the motor is unable to turn the valve to the fully open position, it is not reaching its "end switch" position, so it keeps trying to open the valve. Most likely you need to replace the unit.
Question: upstairs heating zone won't turn on or doesn't receive heat
My upstairs heating zone is not turning on this year. I have checked the setting on the Electronic Aquastat L 7124/L7148 and can not find anything amiss. What might I be missing? - Lisa 12/30/11
See AIRBOUND HEAT SYSTEM REPAIRS
Question: two zone boiler, single circulator pump replaced, now one zone doesn't heat
I have a two zone boiler with a single circulator pump that was recently replaced. I'm now having trouble with ciculation for one of my zones. I think its the zone valve itself though when the thermostat calls for heat I see the valve adjust and I can also set the arm into manual. My question is, is there a way test further if the valve is faulty. My instincts say if I can set the valve and it responds to the thermostat then its not faulty. Thanks - Chris 2/12/12
Chris, as the circulator pump is running (else your working zone would also be cold) I suspect that either the zone valve is stuck shut or that zone is air bound. You are right that setting the room thermostat up above room temperature should cause the valve to open, but if the zone valve itself is jammed or if the zone is air bound you won't get heat.
Question: Taco zone control valves 571, 573 led to short heating cycles
I Installed two Taco zone controls 571 & 573, and now I have short heating on cycles. I never had this problem before, for 47 years. I had to replace the zone controls because the old zone valves started to stick, but they were not Taco brand. I replace the thermostat with a Honeywell TH3000 series, but that didn't solve the problem. - Anon
When the thermostat calls for heat the zone valve opens and the circulator starts pumping. It is the temperature of the water in the boiler that turns the burner on and off. By short cycling I presume you're meaning that the boiler stays on for just a short time, turns off, then quickly turns back on. Sometimes this is a normal event, for example when the first surge of cold water from zone 1 hits the boiler and turns it on, the boiler's burner may be able to heat up the boiler quickly and shut it off; the boiler would stay off for a while. But when zone 2 then opens and sends a new surge of cold water into the boiler it will start again quickly in response to that new temperature drop.
However, because it normally takes some time for the heating zones to actually satisfy the thermostat, once both zones are running your boiler should return to normal run times. If it doesn't I suspect a sensor or control problem at the boiler.
Question: boiler temperatures are too high and the circulator pump malfunctions
Our burner keeps getting hotter than 190 degrees and the circulator has been replaced six times in the last four months. Our aquastat has also been replaced. We had a double then a triple installed. The aquastat currently in place is an electronic hydrostat. The wiring to the burner has been replaced. What can be causing the Taco circulator to malfunction or the burner to get hotter than the settings on the aquastat? - Andrew D'Agostino 4/25/12
Andrew, 6 circulators in 4 months sounds quite odd and as if no one found the real problem. I have seen repeat curculator failures when the tech replaced just the motor or pump but left a bent or worn support that torqued against the shaft bearing and ruined the replacement. If course, limited to no onsite assessment i am not sure what's going on.
Question: Two zone valves on boiler, but one won't go on unless the other one is also on
I have 2 zone valves on my boiler and zone1 will not go on if zone2 is not on. When zone 2 is on everything works good.Is this a bad valve or a wiring issue. - Frank 10/8/2012
Frank, if you mean that the zone valve itself does not operate or it's end switch does not turn on the boiler unless another zone valve is on then it's likely to be a wiring problem. Watch out for the case of two different zone valve brands - sometimes their wiring hookup details are different.
Question: zone valve installation diagram
I need diagram for install zone valve - Manuel 10/8/12
Manuel, we don't know if you're asking about piping routing, zone valve location, or zone valve electrical hookup. The wiring for zone valves varies slightly among brands and models - and will be shown in several options on the instructions that came with your zone valve. As you are installing a valve, look in the box. I know, some fellows use the instructions to kneel on during work at the boiler, rather than reading materials. If you've lost the instructions, give us the zone valve brand and model and we (or you) can obtain the detailed instructions from the manufaacturer.
Typically there are four wires at the zone valve.
Two wires connect from the room thermostat to tell the zone valve to open or close in response to room temperature. They may be marked T1 and T2. Two other wires connect the zone valve end-switch (a switch that closes to make the circuit when the zone valve itself is fully open or shut) to the circulator relay. Those may be labelled C1 and C2.
Question: why should my bathroom heating zone always be calling for heat?
I am not sure if bathroom zone should always call for heat when no other zones ever call for heat unless I turn them up - Steve 10/12/12
Steve, Properly wired each zone normally calls for heat independently.
If your bathroom zone is always calling for heat, check for a short circuit in its thermostat wires, or for a defective thermostat, or a thermostat set higher than the room temperature.
Question: indirect fired water heater is making water that is too hot
We have an oil fired boiler situated on the ground floor which supplies heating to our radiators and also supplies hot water to our bathrooms and basins from a hot water tank situated in a cupboard on our landing. Recently the actuator to the hot water system seemed to fail as the water was becoming very hot irrespective of whether the hot water was on or off at the control panel situated by the boiler as long as the central heating was set at "on". I replaced the actuator to the hot water and it seemed to be ok for a while but then the problem recurred Can you advise please? The only thing I can think of is that recently our son in law opened all the valves to drain the hot water so that he could re-washer a hot tap. This may or not be relevant though. - Roger Cotton 10/28/2012
Question: 100 Series gas boiler is not heating all parts of the house
Have a 100 series gas boiler. Part of the house gets heat but part of the house isnt getting heat. Worked for about a week and stop working and cant figure out the problem. - Brand 11/4/12
Question: After service following flooding from Hurricane Sandy, our boiler keeps running almost constantly
After an annual maintenance visit I noted very hot water and the furnace running almost constantly. They replaced zone valves and charged me. I recently evacuated my house to avoid hurricane sandy. When I left I turned off oil burner and and turned off thermostat.
Zone Valve Issue:
Question: how do I wire one zone valve to cause another one to turn on?
How do you wire one zone valve to another. One controls the other? - Joe 11/22/2012
Question: Our opstairs zone makes noise as if it is opening, and the boiler turns on, but we don't get any heat
I have 2 zones to my furnace basement zone works , but the zone upstairs makes noices as if its working furnace kicks on (2 mins) but no hot water going thru pipes ... Help! - Terri 11/26/12
If your zone valve is actually opening and the circulator is running but the zone doesn't receive heat, it may be air bound. See AIRBOUND HEAT SYSTEM REPAIRS.
On the other hand, the zone valve motor may be making noises but the valve may be stuck and need replacement.
Question: trouble wiring up different zone valve controller brands together
Hi, I have a HE II WeillMcClain nat gas boiler. A few years back I converted about 1/4-1/3 or my house into hydronic radiant floor heat running off same zone as the baseboard. The guy who sweated the tubes and zoned it out has never come back to hook up the zone controller. Someone else came out the other day to hook it up. I have a TACO SR502 2-zone controller and this person purchased a Honeywell L6006C 1018 aquastat controller. I am thinking he purchased the wrong aqua stat. He said the whole system will never allow for 2 zones. I spoke w/techs @both TACO and WeilMcClain who, both said, I can have my floor heat operate separately from the BB units. (I do have 2 thermostats). Can you shed a little light on this, please? Thanks, - T.B. 10/27/2013
Reply: known problem; check with the manufacturer, the wiring diagram, or send us more details
Absolutely, if properly wired, you can take a single loop of hot water baseboard heat and subdivide it, giving each sub-loop its own thermostat and zone control valve.
I have moved the details of this discussion to a new article ZONE VALVE WIRING where I give specific wiring examples for multiple zone valve installation and where I give more details about how we wire up "incompatible" brands of zone valves on the same heating system.
Questions & answers or comments about zone valves on hot water heating systems: installation, diagnosis, repair advice.
Ask a Question or Enter Search Terms in the InspectApedia search box just below.
Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.