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?
Use of air exit tanks and circulator pumps on heating boilers
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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.
The heating system circulator pump, such as the trio of pumps shown at the top of this page, is used to move hot water from the heating boiler out through
one or more loops of piping in a building, through heating devices such as radiators, heating baseboards, or convector units, then
through return piping back to the heating boiler. When the water temperature drops to a pre-set level the heating boiler will re-heat
the water.
The circulator relay is an electrical switch which, in response to a request for heat from a thermostat, turns on the circulator pump.
Some heating systems use a single circulator to move hot water through the building's heating devices. In a one-circulator system, the
building may still divide its heat into various zones or sub-areas of individual heat control, by using either individual radiators in
rooms or perhaps by using electrically controlled zone valves which open and close flow of hot water through sub-loops in the building
heating piping.
Some heating systems use multiple circulators to provide heat to individual building areas or "zones". In this case each heating zone
will have its own thermostat which, acting as a low-voltage "heat on-off switch" will turn on individual circulator pumps when heat is
desired in that zone.
Less common are mixed heating zone systems in which multiple circulators are used but one or more of the circulators feeds a heating
water pipe which is subsequently divided into additional sub-zones of heat control, each sub-zone being controlled by a zone valve.
Which is better: heating control using zone valves or heating control using individual circulators?
Either approach to individual heating zone control can work just fine - using zone valves or using individual circulators.
Some heating contractors prefer using individual circulator pumps, one per zone, perhaps because they recall the history of
unreliable zone valves which tended to clog or jam in some models by some manufacturers. The "zone valve" fellows retort that
modern heating zone valves are as reliable or more reliable than [some models of] heating circulator pumps and that a zone
valve costs a lot less.
Adding zone control to an existing heating system may be less costly by adding a zone valve than by adding a circulator pump.
What goes wrong with hot water heating circulator pumps and circulator switches?
Before assuming the heating system is not working when the thermostat is calling for heat, feel the radiators or baseboards to see if they are getting hot. On a call for heat at the thermostat, if the heating boiler is already hot (above the lower limit or cut-in temperature) then the circulator should turn on and move hot water to the baseboards or radiators. Only after the boiler temperature drops below the cut-in temperature will the heating boiler turn on to re-heat the water. The connection between the thermostat and the heating boiler turning on or off is indirect. On most heating systems the thermostat turns the circulator pump on or off and the temperature of the heating water turns the heating boiler on or off.
The circulator pump may not be running at all. The result can be no heat delivered to the occupied space, or heat may be delivered but only very slowly, as hot water is rising through the heating system by convection rather than being forced (more quickly) by the circulator pump assembly. Because some circulator pumps are very quiet and may have no visibly moving parts (Taco® for example), below we explain how to determine whether or not the circulator is working at all.
The circulator pump may be running but heat does not enter some building areas - part of the system may be air-bound. We introduce this topic below and explain how to correct an air bound heating system at Air-bound boilers & radiators
The circulator pump may be noisy - which could indicate that a bearing is failing - you may need a new pump soon.
The circulator pump may be leaky - often leaks occur at the circulator pump mounting flanges - a leak we describe in detail below.
The circulator pump motor may run but the pump may not be moving water - this less common fault occurs if the circulator pump vanes or other internal parts have become damaged. The motor will run but the circulator does not pump. If the circulator motor runs but there is no temperature change on the heating system piping on the inlet and outlet side of the pump then this could be the problem.
If the boiler runs but the heating baseboard or radiators in an area do not get hot, the problem could be
The thermostat - where multiple thermostats and heating zones are installed, the boiler may be running but the thermostat for a given zone may not be calling for heat; or the boiler may be running to make domestic hot water and even a single zone may not be calling for heat. See Thermostats.
The zone valve - may be stuck closed, if your system is using zone valves. See Zone Valves
The heating system may be air-bound - part of the system piping, baseboards, convectors, or radiators may be air-bound. We introduce this topic below and explain how to correct an air bound heating system at Air-bound boilers & radiators
The circulator pump itself may have stopped working - some common circulator pump brands shown at this website in our diagnostic articles include Bell & Gossett™, Grundfoss™, and Taco™ - these are discussed below.
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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 design, inspection, and repair, and about indoor environment testing, diagnosis, and cleanup are at the InspectAPedia Bookstore.
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.)
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