Heating Boiler Zone Valves
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Install,wire, troubleshoot or repair a zone valve

What is a Zone Valve on Heating Systems?

Summary of What a Zone Valve Does to Control Heat

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.

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).

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.

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.

Other brands of zone valves such as those made by Flair (TM) (problem prone - shown below), 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 MANUALS & WIRING INDEX where we give free PDF downloads of nearly every brand of hydronic (hot water) heating zone control valve.

Below: an obsolete but still-working Flair zone valve with its yellow plastic cover.

Below: we show the same Flair zone valve with its plastic cover removed to show the motor, actuator, and wiring.

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.

Zone Valve Defects Checklist

• Zone valve does not work:
  
  jammed, stuck, does not open in response to call for heat at that zone.
  
  Provided the wiring and thermostat are correct and operating, if no hot water flows past the valve on a call for heat (feel the pipes for heat) it may be jammed and need replacement
  
  Our photo shows the manual control valve in its "automatic" or normal position on a Honeywell™ heating zone control valve.
  
  See ZONE VALVE LIFE Affected by Boiler Water Chemistry below
• Zone valves installed on the hot side or boiler:
  
  out side of the heating piping loop, exposing the valve to higher and more stressful temperatures
• Zone valve installed backwards:
  
  the valve must be installed so that the arrow on the valve body matches the direction of flow of the hot water.
  
  See ZONE VALVE BANGING or BACKWARDS
  
  Water hammer, discussed in general
  
  at WATER HAMMER NOISE DIAGNOSE & CURE
• Zone valve with covers off:
  
  may indicate overheating and jamming
• Zone valve with its manual lever left in the manual "on" position:
  
  may indicate that the valve does not work - this zone is forced into "always on" status.
  
  In our photo above, that notch at the left end of the zone valve control lever will "lock" the valve in the open position.
  
  In normal, not-locked-open operation, the lever will move from left to right in the horizontal slot as the zone valve motor opens (lever to left) or closes (lever to right) the valve.

Below: Flair zone valves.

• Stuck Zone Valves: Older models of some zone valves: 
  
  such as the three older Taco zone valves, models 555-573. shown above are perhaps more likely to be "stuck" either open (you'll have heat in that zone) or shut (that zone won't heat).
  
  Working on older systems I (DF) often found Flair zone valves that had jammed. A clue was seeing a Flair zone valve with its cover left off - illustrated at WHAT IS a HEATING ZONE VALVE?
• Uneven zone heat distribution: 
  
  among multiple zone-valve controlled heating zones:
  
  Because heating zone piping and zone size or zone area heat loss may vary widely within an individual building, if we cannot regulate the hot water flow in individual zones we may find that when more than one of the thermostats are calling for heat at once, some building areas may be too cold while others may be too warm.

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.

• Zone valve is leaking:
  
  leaky zone valves will stop working soon and need replacement. Example:
  
  Norby  said: (2/1/2014)

  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?

  Reply: Norby,
  
  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.

• Zone valves overloading their power transformer:
  
  powering too many zone valves from a single low voltage transformer can damage both the zone valves themselves as well as the transformer.
  
  

  Reader Comment: details of excessive VA load on a transformer

  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'll 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. - Andre

  Reply:

  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 should also see inspectapedia.com/heat/Low-Voltage-Transformer-Test.php
  
  LOW VOLTAGE TRANSFORMER TEST
  and
  also see ZONE VALVE MANUALS & WIRING INDEX

5 Simple Zone Valve Diagnostic Steps

1. Mechanically-stuck zone valve motors.
   
   If your zone valve has a manual override lever you can test the valve to see if it will open and shut. (Our Honeywell zone valve photo above shows this mechanical lever. The Flair zone valves at left do not have this feature).
   
   If the valve can be operated mechanically but does not operate in response to the thermostat we suspect that there is
2. A bad zone valve drive motor :
   
   the valve is not mechanically stuck but the zone motor won't operate the valve. Time for a new zone valve.
3. Faulty zone valve wiring connections or thermostatic control.
   
   Watch out: different brands of zone valves may require different wiring hook-ups and a mix of zone valve brands can lead to some head-scratching in figuring out proper wiring.
   
   I can't give a general solution to this problem as we need to look at the wiring diagram. But yes, the problem can be solved.
4. No electrical power to the zone valve unit
   
   or to the thermostat that controls it
5. Air-bound hydronic heating system:
   
   if the zone valve appears to operate properly but heat never arrives in the zone it controls,
   
   check that the system circulator pump
   
   (CIRCULATOR PUMPS & RELAYS
   
   is working (pump motor hums & moves, pipes get hot on both sides of the circulator inlet and outlet).
   
   If the circulator pump is spinning and the zone valve is open,
   
   see AIRBOUND HEAT SYSTEM REPAIR by WATER FEED VALVE.

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).

Banging Heating Zone Valve: Backwards Zone Valves

Cures for Heating Boiler Water Hammer Noise at Zone Valves

Water hammer, discussed in general

at WATER HAMMER NOISE DIAGNOSE & CURE, can occur in both building potable water supply systems (sinks, tubs, showers) and also in hot water heating systems as well as at water heaters or calorifiers.

At any water heating equipment, such as a heating boiler or a water heater, water hammer risks an additional hazard besides noise: water hammer can cause leaks at the temperature/pressure relief valve.

And over time a relief valve that leaks can also clog from mineral deposits and - to put it technically - crud on the valve seat. A clogged relief valve means that the heating equipment is unsafe to operate, risking a BLEVE.

See BLEVE EXPLOSIONS for details.

If your heating system is giving a loud BANG when the zone valves open or close (and circulator starts or stops) take a look at the location of the zone valves.

Good practice locates the zone controls and circulators on the return side of the hydronic heating loop.

There's theory that the slightly lower temperatures give longer component life and that this location will reduce water hammer noise in the heating zones.

By locating the circulator downstream from the return-side zone valves - that is, between the zone controls and the boiler, the impact of the pump start-up on the zone valve is reduced.

If you continue to have annoying water hammer banging when the circulator pump starts (or stops) consider changing out your zone valves to a slow closing valve such as the Taco #570.

What's wrong with installing a zone valve backwards

What is the downside to installing a 4043 zone valve backwards? - 6 Nov 2015 merlejan

Reply: List of problems caused by zone valves installed backwards include banging pipes and reduced valve life

Merle

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 INSTALLATION GUIDE [PDF]

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:

• The zone valve (installed backwards) may have trouble closing against the force of water being pushed or pulled by the circulator pump - a likely problem since in a zone valve system typically one circulator serves multiple zones (and zone valves)
• A flow restriction if you install the valve backwards
• Banging heating pipes and possible valve damage when the valve closes as a consequence of load on or wear of the mechanically-operated valve gate
• Banging heating pipes when the valve is closing or closed while another heating zone is calling for heat (more likely with fast-closing zone valves and with zone valves on zones operating at higher pressure or faster water circulating rates) (Some experts opine that a White Rodgers zone valve is more quiet-operating)
  
  See WR zone valve manuals at WHITE RODGERS CONTROLS & MANUALS - all
  
  I would not recommend modifying a bangs-at-closing zone valve by removing or weakening its closing springs as doing so is ultimately likely to lead to premature valve failure-to-close. I figure that the manufacturer wouldn't have put parts (springs) in the valve if they were not needed.
• If the actual valve is a "paddle valve" type closure the valve may not open and close properly and may flutter, bang, or jam.

Common Sources of Banging Pipes on Hot Water Heating Systems & Water Heaters

To be fair, not all banging noises originate at a backwards zone valve. Here are other sources of banging noises in buildings:

• APPLIANCE NOISE DIAGNOSIS
• BANGING HEATING PIPES RADIATORS
• BANGING WATER HEATER
• BANGING WATER PIPES
• WASHING MACHINE NOISE CAUSE & CURE

At WATER HAMMER NOISE DIAGNOSE & CURE we cite these other banging heating pipe sound sources

• Poorly-supported heating pipes - long loose floppy piping runs (leaks likely)
• Thermal expansion of pipes through tight building passages
  
  See SOUND CONTROL for PLUMBING
• High velocity hot water circulators combined with fast-closing zone valve models
  
  See CIRCULATORS VARIABLE SPEED
• Air in the hot water heating system
  
  See AIR-BOUND HEATING SYSTEMS - home
• Water hammer anywhere in a hot water heating system or in the building plumbing system (also a function of water velocity and valve closing speed.
  
  See WATER HAMMER NOISE DIAGNOSE & CURE

Reduce zone valve closing speed to stop water hammer?

is there a way to reduce the speed at which the valve closes limiting water hammering? -On 2022-09-27 by jeremiah

Reply by InspectApedia (Editor) - "is there a way to reduce the speed at which the valve closes limiting water hammering?"

@jeremiah,

I have not seen any heating zone valve that offered a variable closing speed, though usually those valves don't close very fast anyway.

If you are having water hammer problems and you're sure it's from the zone valve, then you might try adding a water hammer arrester on the zone near the valve.

Details are at

WATER HAMMER NOISE DIAGNOSE & CURE

Diagnose & Fix a Heating Zone that is Stuck "ON"

I'm having persistent issues with my hydronic boiler system, specifically the downstairs zone is always stuck on, full blast.

My system uses a single boiler with multiple Honeywell control valves.

I've inspected the downstairs zone valve, and it's always open.

I've replaced the motor, and have removed/inspected the spring actuator that closes the valve, and it seems to be operating as it should.

When I detach the valve wires, it closes. When I re-attach them, the valve instantly opens, regardless of what the downstairs thermostat is set to.

The downstairs thermostat could be set to "off" and the control valve still opens up as soon as I reconnect the wires.

Initially I thought the valve motor or spring actuators were not working properly, but in light of what I'm seeing now, I'm wondering if my thermostat is the issue.

I believe the thermostat is a Honeywell TH4110U2005, however I don't see an exact model number or name on the unit.

My house doesn't have AC, so the thermostat only does heat.

Does anyone have any idea as to what my issue could be? The valve seems to work in every regard, but for some reason it thinks it always needs to be open. I've tried giving it some time, to see if it starts working eventually, but this doesn't work either.

The downstairs just keeps getting hotter and hotter until I disconnect the wires, which causes the valve to shut.

I've attached a photo of my zone control valve. - On 2022-09-22 by Anonymous

Reply by InspectApedia (Editor) - downstairs zone is always stuck on, full blast

@Anonymous,

Most zone valves are designed to be normally closed, and open on a call for heat from the thermostat, but there are some zone valves that are normally open and use a signal to close the valve.

Help me out by posting a photo or just telling me

1. the specific problem-zone valve model - Honeywell Model# ?

2. do you have other identical valves installed that are behaving normally?

If so, and given that you say the valve closes when you remove the thermostat wires, I suspect that either the thermostat is itself calling for heat - or jammed or defective - or the thermostat wires themselves are shorted together.

Go to your thermostat and disconnect the wires there

Then go to the zone valve and disconnect the wires there

Then at the zone valve end (you could do this from either end but I'm saving you some running back and forth), using a DMM or VOM see if there is continuity between the two thermostat wire ends.

If so, they're shorted together somewhere en route between the thermostat and the zone valve

If not then I suspect the problem was at or in the thermostat itself

Give me the added details and let me know what you find.

If you need help on using a DMM or VOM in Ohms mode search InspectApedia for USING a DMM SAFELY

Remember to also review the diagnostics at

HEAT WON'T TURN OFF - the problem might not be the zone valve.

Followup by Anonymous

@InspectApedia (Editor),

Thanks for the reply. I've attached a photo of my zone valve, however I'm not seeing an exact model # listed any where that I'm able to see.

I did as you said and detached the wires from the control valve, as well as at my thermostat, and performed a continuity test with my multimeter set to ohms.

I'm using a Gardner Bender GDT-3190 digital multimeter set to "200" ohm). Forgive me for any silly questions - I'm not experienced with using a multimeter.

The reading seemed to stabilize around 20. Does this indicate that I have a wiring short somewhere, or is this likely a thermostat issue?

Reply by InspectApedia-911 (mod) - using a DMM or VOM see if there is continuity between the two thermostat wire ends

@Anonymous,

With the thermostat wires disconnected from all terminals at both the thermostat and at the other end at your heater, will you put your digital or analog multimeter in ohms or resistance mode you should see infinite resistance when you touch your two test terminals individually to each of the two wires.

That is there should be no continuity between them at all.

If there is no electrical continuity between two wires whose ends you are touching with each of your two meter leads then the resistance would read as infinite.

If the two wires were actually connected together somewhere then the resistance would read close to zero.

What can cause confusion is if you forget to disconnect the wires from an electrical device because in that case you're reading some resistance through the device itself.

If you're seeing low resistance like 20 ohms, then there's probably a short between the two wires somewhere in there routing.

Followup by Anonymous

Thanks for the information. I know this may be above and beyond the advice that you typically offer, but do you know if it's typically possible for a heating guy, or an electrician maybe, to pull a new wire through the path of the old wire?

Or, would I need to rip out the old drywall and plaster wall material in order to install a new wire from the thermostat to the utility room?

I have an old house (1925), and unfortunately the utility room and the thermostat are on almost opposite ends of the house, on separate floors.

Can I Lock the Zone Valve Open to flush my heating system pipes?

Photo above: with the zone valve latch moving freely as shown, the zone control should open and close the valve in a response to a call for heat. If you pull the lever to the left and latch it "down" the zone will remain open continuously.

Our reader asked:

I would like to flush my hot water baseboard CH system.

Can I lock the zone valves in the open position when I turn the power off to the boiler and circulating pump without damaging the zone valves or their actuators?

This would be for the duration of the flush, perhaps an hour or two. -On 2023-05-11 by Carr

Reply by InspectApedia Publisher - flush my hot water baseboard CH system

@Carr,

Yes, some zone valves like some of the Honeywell models we show in these articles have a lever that can be slid over and locked in a manual or open position without harming the valve at all.

However you may need to move the lever with a tiny bit of patience as there's some force required to push it from closed to the locked open position. it just takes a moment.

Watch out: why are you flushing out the heating system? Normally that's not necessary.

Boiler Component & Heating Zone Valve Life Affected by Boiler Water Chemistry

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]

Details on the risks of damage or component failure from dissolved oxygen in heating system water as well as suggestion on avoiding those hassles are now found

at DISSOLVED OXYGEN DAMAGE CONTROL.

Zone Valves on Indirect-Fired Domestic Hot Water Heaters

Sketch above: courtesy of Carson Dunlop Associates, a Toronto home inspection, education & report writing tool company [ carsondunlop.com ] showing an indirect-fired water heater (left) being heated by the home's heating boiler.

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.

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.

Number of Heating Zones: How can I determine how many heating zones I have?

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

Reply:

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 ARTICLE INDEX the bottom of this article )

Heating Zone Valves: Normally-Closed vs Normally-Open Designs & Applications

Should you swap out Honeywell V8043D 5080 normally-open zone valves that keep failing?

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.

Reply:

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

Follow-up:

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

Reply:

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 control 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:

• The F and G models of this zone valve include an end-switch to permit switching auxiliary equipment such as a water circulating pump.
• Honeywell V8043D - normally OPEN (your valve) PN 4000396014 has NO END SWITCH - the installation presumes that the thermostat or other control is activating the circulator pump. This is the only one of the four models in this series that is a normally-open zone valve.
• Honeywell V8043D - normally CLOSED PN 4000396013 has an end-switch that will be used to activate a circulator or circulator relay.
• The Honeywell V8043F has these same features. It's safer to refer to the F model but I found it listed both ways. It pays to read the specs.
• Honeywell V8043C - PN 40003916011 normally closed, also has no end-switch.

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

Follow-up:

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

Reply: dissolved oxygen in heating boiler water can cause zone valve failure

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.

See CHEMICAL TREATMENTS, BOILER

Where to locate the zone valves

Where would a valve for the basement in a four zone heating system be - On 2023-05-10 by annmarie

Reply by InspectApedia Editor - How to find the zone valve controlling a basement heating zone

@annmarie,

I think you're saying that heating for your whole building is divided into four zones, one of which serves the basement.

How to find the zone valve controlling a basement heating zone

The zone valve could, unfortunately, be anywhere on the loop of hydronic heating water that heats the basement, but usually the zone valve is close to the boiler, preferably on the piping that is returning to the boiler (as that's the cooler side of the heating loop).

So to find the basement heating zone valve let's

1. identify which pipes heat the basement - do this by turning the basement heat thermostat all the way UP.

That should cause the zone valve for the basement to open (wherever that pesky valve is hiding) and then to turn on the circulator pump and hot water should start circulating from the boiler through the basement heating zone pipes. As boiler temperature drops the boiler's burner should come on, too.

It'll be better if for the time being all of the other heating thermostats are turned all the way DOWN so as to not call for heat.

2. Now feel the various heating zone pipes ( don't get burned!) leaving and returning to the boiler.

The hottest pipe will be the active heating zone - that should be the basement zone

3. Now follow that pipe out of and back into the boiler by eye as much as you can. You should see a zone valve on that pipe.

If you're not sure what a zone valve looks like, check out the photos above on this page and in other articles in this series.

Post a photo of what you find so that we can comment further.

Thank you for a helpful heating question.