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 article series 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.
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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.
Stuck Zone Valves: Older models of some zone valves such as these Flair™ valves are perhaps more likely to be "stuck" either open (you'll have heat in that zone) or shut (that zone won't heat).
The heating system installer or service technician addresses this heat imbalance by fine-tuning the volume or the rate at which heating water is delivered to different building areas. She or he does this by installing and adjusting manual or automatic zone balancing valves or zone flow control valves of various types.
See CHECK VALVES, HEATING SYSTEM for details.
I have a zone valve dripping and when the thermostat turns on the zone valve spins and won't stop on open. It will close when the thermostat shuts off. If I disconnect the wiring and leave the zone valve open will it only pump water thru that zone when another zone is open and making the pump run?
When a zone valve is dripping from the solder or sweat connections it may be possible to repair it - but that'll usually require draining water out of the zone piping first. If the valve is dripping from the valve assembly or motor it's shot and needs replacement.
If the valve spins but doesn't open I suspect the motor shaft is broken - in which case it might be possible to open the valve using the manual latch if your model has one. In that case if the circulator runs hot water will circulate. You can know that the valve is open if hot water is felt in the pipe on the output side of the zone valve.
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 the 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.
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.
6 Nov 2015 merlejan said:
what is the downside to installing a 4043 zone valve backwards?
A slow-closing type zone valve may cause banging heating pipes if installed backwards. Here are some details:
Honeywell, for example, says the zone valve "... must be installed so that the arrow stamped on the body corresponds to the flow direction". - Honeywell V8043D zone valve [PDF installation instructions]
The instructions don't say why but from my reading and field experience I warn that if you hook up a heating zone valve backwards, depending on several other variables including zone valve brand and model and type as well as water velocity there may be trouble:
To be fair, not all banging hot water heating pipe noises originate at a backwards zone valve. At x we cite these other banging heating pipe sound sources
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).
Watch out: for boiler water chemical conditions that could contribute to zone valve failure. These include highly-corrosive water, improper pH, and water with a high oxygen content.
[The Honeywell Honeywell V8043 series zone valve is ] suitable for glycol/water mix up to 50:50 use in closed hydronic systems. Not for use with oxygenated water, potable water or steam.
Use this valve in hydronic systems which DO NOT contain dissolved oxygen in the system water. The dissolved oxygen, which is found in systems that have a frequent source of make-up water, causes the rubber plug inside the valve to deteriorate and eventually fail. - Honeywell V8043D zone valve instructions [PDF]
Indirect fired hot water heaters, in some designs, use a heating coil located in the bottom of the hot water tank to heat the domestic hot water (used for washing and bathing).
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.
I took a look at the boiler. I see the 5 zones going off the outbound pipe, but I only see 2 converging back to the intake. Do you think that means the zones are not all individual loops? - Lisa
Most likely you have
5 individual room thermostats
5 individual heating zones
5 loops of hot water heating piping leaving the boiler (one at each zone valve)
but at some convenient locations the installer joined several of those individual zones into one of two return lines - that's why you see just two hydronic heat (hot water) lines returning to the boiler.
You can still drain and turn off 3 of the zones but you'll need a plumber to find the END of each of the loops you want to turn off - right where it joins a common return line. There s/he will install a drain and control valve. It may be necessary to add air bleeder or air purge valves to permit draining of individual heating zones.
See AIR BLEED VALVE INSTALLATION
The risks of turning off heat completely, besides my previous warning about not getting all the water out, are that you freeze up plumbing somewhere. If the zones do NOT heat any rooms with plumbing you may be ok.
An alternative, and the one that I use, is to keep all 5 zones working, but set the thermostats for the three unused areas to a lower than usual temperature, just high enough to avoid freeze-ups - say 45 °F. You'll save significantly just by dropping the thermostat set temperature.
In an unfamiliar home I might try dropping the thermostat set temperature gradually in very cold weather, double-checking to see just how cold the room gets. You'll want the zones to run occasionally to protect against freezing.
Finally, for freeze protection advice for the building, see WINTERIZE A BUILDING ( a link I'll add at the "More Reading" links at the bottom of this article )
Dennis B. Hoff said: (2/3/3014)
We have a hot water boiler with 7 normally open Honeywell zone valves. They are mounted on the hot side of the boiler. We have problems with the valve motors quitting (after about a year) and have to be replaced.
Would it be better to have normally closed valves instead of the normally open ones? They would only require power when heat is called for and may not heat up as much. Your advice would be appreciated. We live in a area with long cold winters.
Dennis, I don't know. I'm not aware of temperature-tolerance differences among the two valve descriptions you cite, and am confused by the query: in my limited experience a heating zone valve is opened or closed by the room thermostat. On a call for heat the zone valve opens. When the call for heat stops, the valve closes to stop circulating hot water.
However if you are going to the trouble of rearranging or re-sweating zone valves at a hot water heating boiler, I'd see if it were possible to put the valves on the return side of the boiler - cooler water temperatures there may improve zone valve life.
If you give us the zone valve brand and model we can research further. - Daniel
Zone valves we are using are a Honeywell V8043D 5080 normally open (held open by spring pressure) When room temperature is reached the thermostat applies power to the valve and it closes, cutting off fluid flow. In the normally closed valve the valve remains closed by spring pressure and opens when the thermostat apples power to it, allowing fluid flow.
When room temp. Is reached the thermostat cuts off power and the valve closes (by spring pressure) cutting off fluid flow. There are also specific thermostats required for each type of valve.
The valves cannot be moved to return lines without a lot of work. I hope this helps. I do not have the part number for the normally closed valve handy. - Dennis
Thanks Dennis, indeed you are perfectly correct: the HONEYWELL V8043D zone valve [PDF installation instructions] is a "normally open" valve while the Honeywell V8043C, F, or G models are "normally closed". Quoting from the company's product data:
The V8043 Motorized Zone Valve provides two-position (open-close) control of supply water for baseboard radiation, convectors, fan-coil units, etc. It uses a two-wire, 24-volt con trol circuit and requires a SPST thermostat. Integral end-switch models permit the sequencing of auxiliary equipment. Quick Fit actuator provides easy snap on and off connection to the valve assembly.
And I agree you'd need to look at thermostats and wiring if changing the zone valve type as a normally-open zone valve requires a reverse-acting thermostat (as you indicated).
It is possible to simply change the actuator heads from the D model to one of the other models - changing wiring and thermostats as appropriate, leaving the actual valve body installed. A thermostat wired to operate a normally-open zone valve (NO valve) will need to be re-wired if it supports operating a normally-closed (NC) valve. Otherwise the thermostat will need replacement.
Before you would change to a "normally closed" zone valve (which is more common at least in residential installations) we'd want to understand how your heating system was designed to work. The installer surely had a reason for the "normally-open" approach.
Is this a residential building? Are there some special heating needs or applications?
I should add these details about the different Honeywell V8043 zone valves:
Honeywell V8043G - PN 40003916012 normally closed has as an end-switch.,
You can obtain the installation guide and ask questions of Honeywell at 1 (877) 663 0316
And about using a normally-open vs normally-closed zone valve: it depends on the application; for example some hot water applications require the valve to be normally open.
Some writers opine that in some buildings we install a normally-open zone control so that " ... in the event of power failure or malfunction the suite won't freeze and bust up the plumbing and heating pipes." - which is a bit unclear to me since in a power failure the heat is off and the circulator pump is off too - nothing is circulating. But you could argue that in the event of loss of heat but not loss of power, you'd gain that advantage. - Daniel
What I understand is with the normally open valve power is required continuously keep the valve closed. I think that this could cause extra heat build up in the motor and cause premature failure along with more power usage. The normally closed valve only uses power to open the valve when heat is called for.The application that we have is residential, but was originally installed when the house was built 29 years ago. It's a good system but we are trying to improve costs and new procedures develop with time. There are no special heating needs or requirements.
Thanks for all of the information it will help us in making a decision. Probably one thermostats at a time. - Dennis
Dennis: thanks for the follow-up. keep us posted. As I noted, unless the valve mechanism itself is damaged, you can just change the power head - leaving the actual valve assembly in place. Quoting the product literature:
Easy servicing because the entire powerhead assembly can be replaced without removing valve body from line. Optional accessory fittings can be provided to facilitate convenient removal of the entire zone valve unit. - op cit.
When changing the thermostat, there are some models that can be wired to operate either type of zone valve: normally closed or normally open. An example we're looking at is the Honeywell FocusPro TH6110D programmable thermostat - it's quite versatile.
It's not clear to me that the added heat from the 40VA transformer wiring that powers this zone valve would normally be sufficient to contribute to the product's failure in the field. The temperatures of the circulating hot water are, in my OPINION more likely to be a factor in zone valve life.
Watch out: for conditions that could contribute to zone valve failure.
[The Honeywell Honeywell V8043 series zone valve is ] suitable for glycol/water mix up to 50:50 use in closed hydronic systems. Not for use with oxygenated water, potable water or steam. Use this valve in hydronic systems which DO NOT contain dissolved oxygen in the system water. The dissolved oxygen, which is found in systems that have a frequent source of make-up water, causes the rubber plug inside the valve to deteriorate and eventually fail. - op cit.
Watch out: however, for wiring errors, short circuits, or a misbehaving low voltage transformer. Those defects could contribute to zone valve failure, as might corrosive or mineral-laden water in more rare cases.
Moved to ZONE VALVE WIRING - live link given just below.
Continue reading at ZONE VALVE WIRING or select a topic from the More Reading links or topic ARTICLE INDEX shown below.
Or see ZONE VALVE DIAGNOSTIC FAQs for help with diagnosing zone valve problems
Or see AIRBOUND HEAT SYSTEM REPAIR by WATER FEED VALVE if your heating zones don't get hot even though the zone valve opens, the circulator runs, and the boiler heats.
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For page loading speed we've moved most of our zone valve questions & answers to a separate ariticle.
Please see ZONE VALVE DIAGNOSTIC FAQs
(Mar 1, 2015) kevin said:
just replaced thermostat zone calling for heat base board are cold still
HEAT WON'T TURN ON in More Reading - ARTICLE INDEX (above)
or the air bound heating system repair at
may help you out - assuming your boiler is running.
I suspect your system is air bound.
(May 7, 2015) Anonymous said:
Baseboard rad line busted.lost glycol.how do I get air out of system
see the step by step procedure at
(July 20, 2015) Robert said:
I have a normally open honeywell zone valve with 24VAC, 5W, 6RPM output motor actuator. The valve closes on when energized. The model is V8043D1205/U. The thermostat is reverse acting. Now, if we turn down the thermostat, the thermostat will send 24VAC to the valve motor and the motor will operate to close the valve.
The valve will usually close in 10-15 sec, but it may take few minutes to reach the set temperature. That means there will be a period when the valve is fully closed but there is still power to the motor from the thermostat - until the set temp is reached. So, once the valve closes fully, what happens next ?? Will the motor keep operating / turning trying to close the already closed valve and damage the gear assembly and also causing overheat in motor that will burn the motor ?? Is there any mechanism inside to stop motor turning the gears once the valve reaches full close position and there is still power to the motor ?? Otherwise damage will result ??
Yep you may need to replace the motor or the whole valve;
1 Nov 2015 Kerry said:
I have a 14zone HWBB system installed during home construction 8years ago. Each room has its own loop and thermostat. I have zones that are hot 10-15 degrees above set points. All check valves were replaced 10/15/15. System worked fine until spring 2015. When I noticed the hot zones
Sorry, I guess my question from yesterday should have been , why are these zones so hot when the thermostats are not calling for heat? Water is somehow bypassing the check valves, which is why I had them replaced. Any thoughts out there?
I suspect that the flow-control check valve at the hot water lines exiting the boiler is either in manual "open" mode or is stuck open.
Also check that the thermostat wires are not shorted together.
1 Nov 2015 Dennis Santoro said:
How many VA transformer do you need to power 4 zone valves
One should do it.
See LOW VOLTAGE TRANSFORMER TEST where you'll find articles about installing and wiring and repairing low voltage transformers.
More help is also at THERMOSTATS, HEATING / COOLING - home and the thermostat wiring articles.
Or see ZONE VALVE WIRING
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