How to tell if a heating circulator pump is working
Why do some heating zones work and others not, why does heat come out of zones where thermostats are not calling for heat?
How to fix an air-bound heating system and blocked circulator pump
Where should a circulator pump be installed on a heating boiler? On the inlet or on the outlet side of the boiler?
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Heating system circulator pump troubleshooting: here we list & describe other heating system controls that manage or impact heating boiler circulator pump operation. This article series discusses Circulator Pumps: how to find, inspect, diagnose, and repair problems with Hot Water Heating System Circulator Pumps
or circulator pump relay switches and controls. Also you will see that
this website answers most questions about Heating System Boiler Controls on central heating systems to aid in troubleshooting, inspection, diagnosis, and repairs. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.
Other heating system controls related to hot water circulator pumps - three alternative ways to control hot water heat circulation
The aquastat is the most common control of heating system boilers. On a call for heat the thermostat, connected to the aquastat primary control, will operate a circulator control relay inside the aquastat to turn on the circulator pump, or on some systems the thermostat may be connected to a separate circulator relay discussed just below.
Our photo (left) shows the interior of a Honeywell R8182D aquastat primary control. The gray rectangle at top center in this photo is the circulator relay. You can just make out the red and white thermostat wires connected to the control at the upper left in this picture.
Our page top photo shows the low on a multi-function aquastat or primary control on a heating boiler. The low switch on an aquastat maintains temperature in a heating boiler that also makes hot water using a tankless coil. The low switch indirectly controls the heating circulator by locking out (keeping off) the circulator pump assembly if the boiler temperature drops into the low range.
Circulator relays on heating boilers - an older and by some heating service technicians, a preferred method to control the distribution of heat to individual
building areas uses a individual circulator pump to force heating water through each individual heating zone piping. This system too is usually found
on hot water baseboard heating systems.
Our photo (left) shows a typical circulator relay with the control's cover removed - thermostat wires are connected at the upper left in this photograph. Line voltage is connected at lower left, and the circulator connections are at lower right.
Two or more circulator relay switches, one relay for each circulator pump, will be installed to turn on and off
each heating water circulator if more than one heating circulator is installed. Individual low-voltage thermostats located in the living area will respond to
a call for heat by switching on the circulator relay which in turns on the (120V) circulator pump.
Individual High Limit and Low Limit relay switches on heating boilers: these may be provided on older heating boilers. See Limit Switches, Boilers
Protectorelays - on older heating boilers a protectorelay or stack relay may be used to control oil burner operation - see Stack Relay Switch
Zone valves on heating boilers - 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.
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).
Air exit tanks on heating boilers and circulator pump mounting location - some heating boilers use an air exit tank mounted on the hot water header above the heating boiler to combine the function of an Expansion Tank with the Air Bleeder Valve or air purge valve to rid the hydronic (hot water) heating system of un-wanted air. Air in the heating system will often rise to a high loop of radiator or heating baseboard piping where it will block the flow of hot water, leading to an air-bound heating system and no heat in some or all of the heating system.
The air exit tank captures and vents unwanted air from its location above the heating boiler on the boiler outlet or supply side. When an air exit tank is used instead of a simpler expansion tank at a heating boiler, the boiler manufacturer may specify that the circulator pump be mounted on the boiler outlet side to improve the function of this device. Thanks to Wayne Hoffman, technical advisor for Raypak, a Rheem company that provides hydronic heating equipment, for this detail.
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"Installation and Operation Instructions, Raytherm Residential Boilers," courtesy of Raypak®, and technical advisor Wayne Hoffman, personal communication 5/11/2009. Mr. Hoffman is a technical advisor with more than 30 years experience in the heating field. Raypak is a Rheem company that provides hydronic heating boilers for residential, pool, and commercial use. Raypak can be contacted at 866-583-0664 for technical support or for assistance in selecting the proper heating equipment for a specific application.
Rheem Corporation is a manufacturer of water heaters and heating equipment including Ruud heating and cooling products.
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 2010, $69.00 U.S., is available from Carson Dunlop. The Home Reference Book is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. InspectAPedia.com ® author/editor Daniel Friedman is a contributing author. Field inspection worksheets are included at the back of the volume.
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 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.)
Links to our list of additional information on heating system inspection, repair, maintenance
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