LARGER VIEW of a heating boiler cad cell relay switchHeating System Zone Valve Troubleshooting
Zone Valve Diagnostic FAQs

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Hot water heating system zone valve diagnosis & repair:

Frequently-asked questions about heating zone valves on hot water (hydronic) heating systems.

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Hot Water Heating System Zone Valve Diagnostic FAQs

Honeywell heating zone valve

These hot water heating zone valve questions & answers were posted originally at ZONE VALVES, HEATING or possibly at an earlier collection of questions & answers about zone valves found at ZONE VALVE REPAIR FAQs-1

On 2017-07-15 by (mod) where to find dissolved-resistant zone valves


Thank you for asking - I've done more research on dissolved oxygen issues for heating systems - please see a detailed reply to your question, now found at


I've asked Honeywell if the company specifically recommends any particular zone valve models as resistant to dissolved oxygen as I haven't found such products. Meanwhile at the article I cite you'll see how industry experts suggest avoiding damage from dissolved oxgyen in residential boilers.

On 2017-07-15 17:56:30.791030 by Denys

Question: are there zone valves that resist damage from dissolved oxygen in hydronic heating system boiler water

Denys Picard said:

Honeywell warns that makeup water feed to a boiler may damage the rubber plug of Zone Valves 8043 and make them fail.

Are they zone valves resistant to dissolved oxygen from makeup water feed? Thank you.

On 2017-07-15 by David

Thank you for the answer and reference research, as I am not familiar with these equipements, I tend to read all instructions carefully. And yes, I have an open loop system that feeds on my softened and filtered well water, but my heating system is well equiped with many automated gas purging devices

.I hope it will be enough to ensure good performance for a reasonable time. I guess that all other brands also do put this caution then.

On 2017-05-19 by (mod) - ticking zone valves


If the valve ticking stops after the system has cooled down I suspect it's thermal contraction; sometimes using plastic noise reducing pipe mounts can reduce or even eliminate that problem.

If the zone valve is ticking continuously and never stops that sounds like a failed or jammed zone motor and the valve head probably needs replacement.

On 2017-05-18 by David

We have a two-port motorised valve that makes a ticking noise when the hot water is switched off.

Is there anything that can be done about this?

On 2016-12-26 by (mod) - no heat: thermostat exposed to drafts? Overheating zone motor?

Perhaps there is a draft r at or in the wall cooling the thermostat,or the temperature sensor could be dust blocked.

If with the motor-head removed from the zone valve you cannot easily open the zone valve then it needs replacement.

If you can open the valve but the line never gets hot, I suspect the line to that zone is air blocked. In that case,search for AIR BOUND HEATING SYSTEM to read repair details.

On 2016-12-26 by Steve

I moved it to manual but it didn't turn over in that zone. So I moved it back. As I raised the other zone upstairs the lower zone started to kick in. That's why I was wondering if it could be the motor of the zone valve.

On 2016-12-26 y (mod) could a bad zone motor explain it sticking?

See if the zone valve is stuck shut; see if you can latch the valve in a manual OPEN position.

On 2016-12-25 by Steve

Hello I could use some advise. I have a two zone heating system. They were both just working fine but now the lower level stays cold and only gets warm when the upper level kicks in. I changed the lower thermostat but the problem persist.

A year ago I had the upper valve changed and it was suggested then that the other one would need to be replaced soon. Does this appear to be my problem now, that I need a new zone valve motor for the lower level.

On 2016-12-22 by (mod) emergency use of the manual open lever on a zone valve or pushing the head down


For emergency heat you can manually open the valve by pushing the "manual" level in the valve head all the way down.

Having replaced the head, did you test to see that the valve body would open and close easily? It may be jamming.

On 2016-12-22 by Stephanie

I have 2 zones both with taco 571 valves. Zone 1 works fine but 2 doesn't. I have 24v on 1and2 and turn up thermostat to 90 but it never opens, and I don't get any volts between 2 and 3. I've tried replacing the head and still nothing? But it works in the open position?

On 2016-12-22 by (mod) - too many thermostats & zone valves on one power transformer


Perhaps 7 thermostats is 3 more than a single power transformer can support - or if the setup uses 2 transformers you may have blown one.

On 2016-12-21 20:53:47.644169 by Al

I have a 7 zone heating system with thermostats. I was trying to replace honeywell thermostat with nest, when i un-installed the thermostat and installed nest, i noticed that i lost power and nest was not functioning.

my other two rooms also lost heat because they are wired to the same transformer(however, the other two rooms have power just no heat). Is this a bad transformer issue or something else?

On 2016-12-13 by George

I have a 7 zone heating system with thermostats. In two of the rooms the thermostat is set a 63, but the heat goes up to 79. What could the problem be?

On 2016-12-13 13:03:05.522294 by (mod) Drayton ZA5 zone actuators & multiple controls

Logically one, either, or both thermostats should work to call for heat. No third control is used. Perhaps one reversed low voltage wires.

On 2016-12-13 08:19:05.911904 by Dafydd

I have added underfloor heating to my system and made it a 2 zone heating system. Both zones operate independently of each other and fire the boiler up as expected but I'm having issues with both thermostats calling for heat at the same time and both valves being closed. I know this will be a wiring issue requiring a signal from somewhere to ensure this does not happen.
My wiring is very close to the S plan wiring.

I have Drayton ZA5 zone actuators
My boiler is a Veissman Vitodens 100
My room thermostats are Honeywell Wireless CM927

I know this is a wiring issue but I can't see to find a solution.

On 2016-11-03 by Mike Rose Taco zone controller

I have a Taco zone controller on my furnace, professionally installed, but the issue is that even after tightening the screws down holding the wires securely, they keep loosening up. Then I notice a zone is cold, go down and tighten them up again and the zone immediately kicks in. Is there some known issue with Taco controls? This unit is mounted on the furnace itself, vibration? Cure? Thanks.

On 2016-06-06 by (mod) thermostats not working right - shorted wires?

Check for thermostat wires shorted together

On 2016-06-06 by Roland

Thermostat work only once wayatwe running I mean always hot water running,no regard the position of the thermostat imean high or low open or closed n.b. brand new motor valve

On 2016-04-26 by Shaun

Had an indirect HW tank go on my gas 3 zone HW system & went with a new set up having an electric HW tank wired direct to my circuit box. Problems of all kinds.
Heat not working. Utica boiler (usc5) will fire up and then shut down after 15 sec or so.

Called hvcc people back and they are now telling me after a $226 service call/estimate that all 3 of my Erie zone valves are bad and need to be replaced. What are the chances of all 3 valves going at the same time? When they cut the pipes to remove the old indirect tank and wired the new tank (by the way they piggybacked it on the panel cause there was not enough room) could that have somehow damaged my 3 zone valves (the 4th was for the old HW tank and pipe was capped but wiring was just left)?

Other bad news is that when i took my 1st bath with the new 50gallon HW tank, the HW stopped about 1/4 of the way in filling and turned cool. What gives? Granted the tub is at the opposite end of the house but the old 40 gallon tank had no problem filling the tub with hot water.

On 2016-01-23 by (mod) zone valves for radiant heat

Check that the zone valve you are using is designed for use with your radiant heat system; also check the low voltage power supply.

On 2016-01-20 by Bruce

The radiant heat component of our heating system was calling for heat 24/7 but the heat was barely trickling in. I replaced the zone valve that was the problem. The new one has the same problem - it only opens partially. I have to manually open it all the way.

It stays fully open until the thermostat stops calling for heat. Both zone valves then close. When heat is called for again, it only opens partially, and, again, the boiler is on almost constantly, with the heat barely trickling in, unless I manually fully open it. Thoughts? Thanks.

On 2016-01-01 by (mod) basic zone valve wiring debugging


This may help:

On a call for heat the thermostat is acting as a simple "on-off" switch. Connected to 2 wires at the zone valve, it tells the valve motor to open to permit hot water to flow into the zone. When the valve motor has turned to fully open water flow, and end switch in the valve control head connects two more wires that tell the circulator to start. That's the usual 4-wire Honeywell zone valve set-up.

If your circulator pump relay is not working then either we've made an error in wiring or the zone valve end switch isn't working.

But there are compatability and wiring errors that come up if we mix two different brands of zone valves on the same system, both of which are trying to turn on the circulator pump. To sort that out we need to know both brands and to look at their wiring instructions.

I've run into this trouble myself - I used to call Dave Ferris at GEM supply in Poughkeepsie and Dave would say "oh yeah - for that, just connect the yellow wire to terminal X" - but Dave has retired.

Take a look at

that may help.

On 2016-01-01 by Denis

The valves are just out of the box. I have only one that is wired for the moment & suspecting a faulty valve head was in my trouble shooting sequence. So I tried on a head from another not yet installed valve & the problem persisted.

As is, the zone is operating beacause as statted before, the valve opens when the thermostat asks it to do so.

But since the pump contactor did not energise, I've used a spare thermostat to feed the it. So 1 thermostat operates the valve & the other one operates the pump contactor who feeds the heating element contactors.I didn't think it would help but I have also inversed the leads at the feeding transfo to no avail.

On 2015-12-29 by (mod) problem with the zone valve control head end switch

This sounds like a problem with the zone valve control head end switch.

Indeed I've run into wiring questions when mixing brands of valves.... more asap

On 2015-12-28 by denis maringouin The Taco zone valve wiring

New taco zone valve does not energise the circ. pump contactor.


I finally figured out why I keep burning out my magnetic contactors that feed the elements in my electric domestic boiler! The Honeywell zone valve end switches cause the magnetic contactors to chatter. As a result, they overheat and burn.

I’ve had technicians change the 2 main contactors 4 times in the past 30 years & they have burned once more. I knew something had to be causing these failures & that it was not just the contactors that where failing so I started investigating & I figured it out that the end switches where the culprits.

I found 2 new contactors on line & also purchased new Taco 571 valves. Replacing the contactors was a breeze but I’m stuck on the valves.

The old Honeywell valves have 4 wires, 2 for the valve & 2 on the micro end switch. The Taco valves have only 3 wires.

The diagram for the Taco valve shows:

- 1 wire from the transformer that goes to feed the thermostat & continues on to the # 1 terminal on the valve.

- The 2nd wire from the transformer goes to

A:- the # 2 terminal on the valve,
B:- one pole on the circ. pump magnetic contactor.

- The 3rd terminal on the valve goes to the other pole for the circ. pump magnetic contactor.

I figure this to mean that; the #2 contact on the valve is common to the thermostat & the circ. pump magnetic contactor.

(a):- the thermostat circuit is completed from the transfo, to contact #2 on valve, out at contact #1, through the thermostat & back to the transfo.

(b):- the end switch circuit is completed from the transfo, to 1 pole for the circ. pump magnetic contactor , to #2 contact on the valve, out contact #3 on the valve & back to the other pole on the circ. pump magnetic contactor.

This means that when the thermostat closes & makes contact, it open the valve which when open should close the end switch that should energise the circ. pump magnetic contactor that in turn should energise the 2 sequenced element contactors.

Well, nothing is ever easy!! It doesn’t work

The valve opens but the circ. pump magnetic contactor does not energise.

Can someone help me? Thanks, Denis.

On 2015-11-24 by (mod) possible bad zone valve motor


The issue can be in the motor - that can be replaced without removing the valve body -
or in the valve assembly itself.

Pull the motor and see if you can easily rotate the valve stem.

On 2015-11-23 by valve sticks on

I find that sometimes one of my zone valves will stick on causing my house to overheat. If I tap it with a wrench, it will click off. Lately it has happened more often so I need to correct it. Do you think I need to replace the whole valve or just the actuator motor assy?

On 2015-11-07 by (mod) unwanted heat in one zone

Look for

- thermostat wires shorted together

- a zone valve stuck open

- a flow control valve at the boiler stuck open or manually in open position

On 2015-11-06 by Fred

I have a 2 zone hot water baseboard the upstairs baseboard is hot with the thermostat turned off

On 2015-05-07 by (mod) stuck zone valve diagnosis


I'm concerned that if the zone valve is stuck open the problem may be in the valve body not the motor. Remove the motor or "head" from the valve and see if the valve itself is jammed. If so the whole valve needs replacement.

On 2015-05-07 by Help

I have a 2 zone heating system (3 if you include the hot water). Zone 1 and hot water work fine. Zone 2 is stuck in open position (Honeywell 8043f, lever has no resistance). Zone 2 only (and always) provides heat if hot water or zone 1 is requesting heat.

However, if Zone 2's thermostat is requesting heat, the circulator and furnace do not come on. This is a one circulator system. I think I have to replace the motor of the Honeywell8043, but not sure, since it doesn't work when the thermostat is requesting heat.

On 2015-02-17 by Jeff

I have a four zone heating system with White Rodgers 1311 zone valves. Recently had a water pump failur. Heating system and all radiators have been bled after water was repaired. Now one zone valve will not open when heat is called for.

If I start the "wheel" manually it will spin all the way around, open and then closed again so the zone won't heat up. Could there be debris in the zone valve? Is there a way to clean it, or keep it open manually as a stop-gap?

On 2017-06-25 19:16:01.891863 by Rob

Can anyone tell me why I have two inline zone valves on my hot water system? And one on my central heating?

On 2017-05-05 by Wayne Rife

The reason the higher contractor wants to replace the piping is to create more work and make more money.

On 2017-04-22 by (mod) switching from an oil burning boiler to a high efficiency gas Bosh boiler

I don't understand what the higher bid contractor is actually thinking; Why would a boiler over-heat; it is controlled by its aquastat settings. Furthermore, what are we talking about here - a matter of seconds, not even minutes, for a zone valve to open.

However if the Taco zone valves are quite old it'd make sense to install new units for reliability. Still why on earth that would require complete re-piping of all of the zone piping leaves me confounded.

For an authoritative answer you could try calling the boiler manufacturer's tech support line - be tactful and taciturn - they won't want to irritate the contractor whom they probably consider their "real" customer.

On 2017-04-22 by David Mills

I am switching from an oil burning boiler to a high efficiency gas Bosh boiler. I have two bids differing by about $1400.

The bids cover the same thing except that the higher bid calls for redoing the piping from the new boiler into the heat zones and replacing the old Taco zone valves with new zone valves that would open instantly when heat was called for, the other bid reuses all the piping as is and retains the old zone valves.

The reason given was that the Taco valves take time to open and that the new boiler would tend to overheat waiting for that valve to open. Is that a real concern or are the Taco valves fine for the new 95% efficient gas furnace?

On 2017-03-11 by (mod) - where are the zone valves located?


Take a look at the photos at ZONE VALVES, HEATING - you can see the mostly silver-covered zone valves - usually located near the boiler and best, on the cooler return-side of the heat piping loop. But a zone valve can be located at more remote spots too if a heating zone loop splits into a sub-loop elsewhere in the building.

The thermostat controls the zone valve, telling it to open or close in response to a call for heat. The zone valve, when it is fully open, closes an "end switch" that turns on the circulator pump - in most designs, though in some countries installers keep the circulator on all the time - in that case the zone valve just opens or closes.

The temperature of the water turns the boiler on or off.

Search InspectApedia using the InspectApedia serarch at the top or bottom of any page, looking for ZONE VALVE WIRING to see typical wiring diagrams for all of the common zone valve brands and types.

On 2017-03-11 by shibu

hi can any body hive zone valve installation working procedure ,where the location in heating systems
thanks shibu

On 2017-02-17 by (mod) are zone valves ball valves?

Yes or stop valves. Most models are not the more-reliable (and more costly) gate valves.

On 2017-02-17 by Bob B

Are these valves just ball valves?

On 2016-12-09 by (mod)

What return, anon? If you mean the zone valve: it's normally fully open or fully closed.

On 2016-12-09 by Anonymous

I just want to know if I should have my return fully open or partially open

On 2016-12-04 by Dan

Thanks , my installer has just come back to me and has also said that it doesn't sound right. I'll see what I can do about a replacement. Thanks for your reply. Dan

On 2016-12-01 16:47:41.029481 by (mod)


Buzzing zone control sounds unusual, perhaps a failing low voltage transformer or a valve that's jamming.

On 2016-12-01 by (mod) taco zone valve is not shutting off when desired temp is reached


If nobody changed the wiring then more likely the valve is jammed open or its motor has failed. Can you manually close the valve? If so, try that. IF you can't move the mechanical valve parts then the zone control needs replacement.

On 2016-12-01 by joe

my taco zone valve is not shutting off when desired temp is reached, it is staying in the open position .is this caused from thermostat wiring into relay being backwards?

On 2016-11-30 by Dan

I've just had 2 zone valves (Sunvic) fitted to separately control under-floor hearing in one room and the central heating in the rest of the house. When the valves open or close there is a loud noisy buzz for 45 seconds or so. Is there such a thing as a silent (or at least very quiet) actuator? The noise is driving myself and Mrs Dan mad... Thanks

On 2016-11-29 by john a - wrong voltage at the thermostat?

I have a 3 zone system on a boiler unit. Each zone has a valve and relay and 1 thermostats. problem is i have a thermo runaway on 1 of the zones, I pulled the thermostat and the radiators for that zone cooled down. I replaced the thermostat and all seemed fine for a day, now back to thermo runaway.

I checked the voltage and i get 75 volts at the thermostat, that does not sound right to me (24 v system). I get 24 volts out of transformer, goes through small circuit board and ups to 75 volts. Is this the operating voltage for the zone relays or valves? what can cause the 75 volts on the thermostat from the system?

On 2016-11-27 by Anonymous


On 2016-10-20 by (mod) voltage drops when 7 zone valves are on one transformer

Good question, Andre.

We often read about people hooking up too many zone valves to a single transformer, overloading it. When updating this article I'll be sure to include your helpful comment.

Readers shoud also see -LOW VOLTAGE TRANSFORMER TEST

On 2016-10-20 by Andre

Just curious about the query whose 7 zone valves keep failing once a year. I wonder what the rating on the transformer is? If it's a standard 40VA like you find on a lot of equipment from the factory, 7 of those valves will try to draw 60VA if they all open at once.

The voltage will sag, the current will go through the4 roof, and you'l burn the windings on those tiny synchronous motors. And this is not just an instantaneous short either - once those valves start going, they keep going as long as necessary. Reader should make sure they have at least a 75VA transformer for the valves - 60VA for full load plus 20% headroom.


Continue reading at ZONE VALVES, HEATING or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see ZONE VALVE REPAIR FAQs-1 for set #1 of heating zone valve diagnostic questions (and answers)

Or see these

Zone Control Articles

Or see ELECTRIC MOTOR DIAGNOSTIC GUIDE to test zone valve motors themselves

Suggested citation for this web page

ZONE VALVE DIAGNOSTIC FAQs at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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