Guide to Heating System Boiler Zone Valve Controls
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Zone Valves on hot water heating systems
Zone valves on indirect domestic hot water heaters
What is a motorized zone valve on a hot water heating system?
How do heating zone valves work, how do we inspect, repair, install them?
Questions & answers about zone valves on hot water heating systems: installation, diagnosis, repair advice

Zone valves on hot water heating systems: what is a zone valve, how do they work, and how do I troubleshoot, install, 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.

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Explanation of Zone Valves on Heating Boilers - Controlling Hot Water Heat

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.

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.

Zone Valve Defects to Watch For

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 (left) shows the manual control valve in its "automatic" or normal position on a Honeywell™ heating zone control valve.
Zone valve is leaking - leaky zone valves will stop working soon and need replacement
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 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

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).

For details about the setting, re-setting, or function of the controls and switches commonly found on hot air heating systems see these articles:

Hot Air Heating Furnace Basic Operating Steps
Guide to Heating System Components:
Air Bleeder Valves for Hot Water Heating Systems: Radiators, Baseboards, Convectors
Aquastats Heating Boiler Primary Controls: A guide to Aquastats for control of hot water heating boilers and tankless coils
BLUE vs YELLOW COMBUSTION FLAMES - the Blueray history and blue flame vs. yellow flame combustion, flame color & combustion efficiency, & how oil competes with gas as a heating fuel.
CAD CELL RELAY SWITCH on oil fired furnaces or boilers as flame sensors & safety devices
Check Valves Guide to check valves and backflow preventers on hydronic (hot water) heating systems (gas or oil fired)
Draft Hoods on gas fired heating equipment, function and safety
Draft Regulators & barometric dampers on oil fired heating equipment
Expansion Tanks Guide to pressure control and expansion tanks on hydronic (hot water) heating systems (gas or oil fired)
Fan Limit Switch on hot air furnace heating systems (gas or oil fired)
Flue Gas Spill Switch on gas fired heating equipment sense combustion and protect from blocked flues
Gas Piping, Valves, Controls including gas regulator assembly and other controls
Heat Won't Turn Off - Stop Unwanted Heat explanation of why heat may continue to come out of radiators or baseboards even though you have turned down the thermostat
MIXING / ANTI-SCALD VALVES: Guide to mixing valves on hot water heating systems and radiant heat systems
Power Switches to turn on or off heaters for furnaces & boilers, oil & gas fired, heat pumps or electric furnaces or boilers
RELIEF VALVES - TP VALVES: A guide to temperature and pressure relief valves & safety controls on hot water and steam heating systems
Stack Relay Switches Explained on oil fired furnaces or boilers as flame sensors & safety devices
Thermostats & Heat Controls for furnaces & boilers, oil & gas fired, heat pumps or electric furnaces or boilers
Water Feed Valves: A guide to water-feeding/pressure-reducing valves on hot water and steam heating systems
Zone Valves: A guide to zone valves for heating zone control on hot water heating systems

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).

Zone Valves on Indirect-Fired Domestic Hot Water Heaters

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.

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.

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Zone Valves - see detailed links at pageleft

Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. Thanks to Alan Carson and Bob Dunlop, for permission to use illustrations from their publication, The Illustrated Home which illustrates construction details and building components. Carson Dunlop provides home inspection education including the ASHI-adopted Home Inspection Training Program (home study course), publications such as the Home Reference Book, report writing materials including the Horizon report writer, and home inspection services. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.
Domestic and Commercial Oil Burners, Charles H. Burkhardt, McGraw Hill Book Company, New York 3rd Ed 1969.
National Fuel Gas Code (Z223.1) $16.00 and National Fuel Gas Code Handbook (Z223.2) $47.00 American Gas Association (A.G.A.), 1515 Wilson Boulevard, Arlington, VA 22209 also available from National Fire Protection Association, Batterymarch Park, Quincy, MA 02269. Fundamentals of Gas Appliance Venting and Ventilation, 1985, American Gas Association Laboratories, Engineering Services Department. American Gas Association, 1515 Wilson Boulevard, Arlington, VA 22209. Catalog #XHO585. Reprinted 1989.
The Steam Book, 1984, Training and Education Department, Fluid Handling Division, ITT [probably out of print, possibly available from several home inspection supply companies] Fuel Oil and Oil Heat Magazine, October 1990, offers an update,
Principles of Steam Heating, $13.25 includes postage. Fuel oil & Oil Heat Magazine, 389 Passaic Ave., Fairfield, NJ 07004.
The Lost Art of Steam Heating, Dan Holohan, 516-579-3046 FAX
Principles of Steam Heating, Dan Holohan, technical editor of Fuel Oil and Oil Heat magazine, 389 Passaic Ave., Fairfield, NJ 07004 ($12.+1.25 postage/handling).
"Residential Steam Heating Systems", Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
"Residential Hydronic (circulating hot water) Heating Systems", Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
"Warm Air Heating Systems". Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
Heating, Ventilating, and Air Conditioning Volume I, Heating Fundamentals,
Boilers, Boiler Conversions, James E. Brumbaugh, ISBN 0-672-23389-4 (v. 1) Volume II, Oil, Gas, and Coal Burners, Controls, Ducts, Piping, Valves, James E. Brumbaugh, ISBN 0-672-23390-7 (v. 2) Volume III, Radiant Heating, Water Heaters, Ventilation, Air Conditioning, Heat Pumps, Air Cleaners, James E. Brumbaugh, ISBN 0-672-23383-5 (v. 3) or ISBN 0-672-23380-0 (set) Special Sales Director, Macmillan Publishing Co., 866 Third Ave., New York, NY 10022. Macmillan Publishing Co., NY
Installation Guide for Residential Hydronic Heating Systems
Installation Guide #200, The Hydronics Institute, 35 Russo Place, Berkeley Heights, NJ 07922
The ABC's of Retention Head Oil Burners, National Association of Oil Heat Service Managers, TM 115, National Old Timers' Association of the Energy Industry, PO Box 168, Mineola, NY 11501. (Excellent tips on spotting problems on oil-fired heating equipment. Booklet.)

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Fuel Oil & Oil Heating Magazine, 3621 Hill Rd., Parsippany, NJ 07054, 973-331-9545
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Explanation of Zone Valves on Heating Boilers - Controlling Hot Water Heat

Zone Valve Defects to Watch For

Zone Valves on Indirect-Fired Domestic Hot Water Heaters

Questions & Answers regarding this article

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