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ZONE VALVES, HEATING
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
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).
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.
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.
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
Most likely you have
Heating Zone Valves: Normally-Closed vs Normally-Open Designs & Applications
Reader Question: do you advise swapping out Honeywell V8043D 5080 normally-open zone valves that keep failing?
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.
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:
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).
I should add these details about the different Honeywell V8043 zone valves:
Honeywell V8043G - PN 40003916012 normally closed has as an end-switch.,
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:
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.
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 shown below.
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Frequently Asked Questions (FAQs)
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Please see ZONE VALVE DIAGNOSTIC FAQs
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