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HEATING SYSTEMS
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    Circulator Pumps vs. Zone Valves
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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.

Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution. © Copyright 2009 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

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.

If the heating boiler itself if does not turn on in a response to a call for heat see NO HEAT - BOILER / FURNACE DIAGNOSIS.

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Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

BOILERS, HEATING
  BOILER OPERATION DETAILS
  BOILER CONTROLS & SWITCHES
  Air Bleeder Valves
  Aquastat Functions
  BOILER LEAKS CORROSION STAINS
  BOILER OPERATING PROBLEMS
  BOILER PARTS LIST
  Boiler Pressure Controls & Settings
  Cad Cell Relay Switch Flame Sensors
  Circulator Pumps & Relays
    Circulator Pumps vs. Zone Valves
    Circulator Pump Trouble List
    Checks for Circulator Operation
    Single Zone Heat Tests
    Multi-Zone One Circulator Tests
    Multi-Zone Multi-Circulators Tests
    Individual Zone Tests
    Un-wanted Heat in Some Zones
    Leaks at Circulators
    Circulator Motor or Bearing Failures
    Where to Mount Circulator Pumps
    Other Circulator Controls
  Expansion Tanks
  Gauges on Heating Equipment
  Limit Switches, Boilers
  Low Water Cutoff Valves, Boilers
  Mixing Valves
  Relief Valves - TP Valves
  Reset Switch - Primary Control
  Reset Switch - electric motors
  Spill Switches
  Stack Relay Switch
  Thermostats
  Water Feeder Valves, Hydronic Boiler
  Zone Valves
  WATER HEATERS
ZONE VALVES

• "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.

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• Weil McLain Model GV Gas Boiler/gas valve CPSC recall/repair
• 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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