Guide to Heating System Boiler Check Valves & Flow Control Valves InspectAPedia® -
Troubleshooting heating system check valves, flow control valves, flo-control valves
What are flow-control valves & how do they work?
What are IFC circulators - internal flow control valves?
What are back-flow preventer valves on heating systems?
How do automatic water feed valves also function as a check valve on heating systems?
Cleaning & maintenance guide for heating systems
Questions & answers about check valves and flow control valves on heating systems
Here we explain heating boiler check valves, also referred to as flow control valves, flo-control valves: controls that prevent hot water from circulating in the heating system when it is not supposed-to. We also discuss IFC circulators - internal flow control circulators, and heating system backflow preventer valves.
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This article explains types of check valves used on hot water heating systems.(If you are looking for information on water supply piping & well system check valves see WATER SUPPLY SYSTEM CHECK VALVES).
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 modern cad cell relay on an oil fired heating boiler - one of the safety controls which we discuss in this article.
Check Valves on Hot Water Hydronic Heating Systems - Flow Control, Flo-Control Valves, Inspection, Settings, Problems
Check valves on heating boilers prevent hot water from circulating through the building when it is not supposed to be doing so - such as when the boiler and its water are still hot but the thermostat has stopped calling for heat.
Why Are the Baseboards or Radiators Hot Even Though the Thermostat is Set Higher than Room Temperature? Un-wanted Gravity or Convection Circulation of Hot Water
If electrical power switch to a hot water heating boiler is in the "on" position (see ELECTRICAL POWER SWITCH FOR HEAT) and the room thermostat is set above room temperature, the heating system (hot water or steam) boiler or (warm air) furnace should not run.
But for hot water heating systems (baseboards, radiators), other defects could cause or permit hot water to circulate through the heating system by "gravity" (convection, warm water rising on its own through the heating piping) even though the thermostat is not calling for heat.
The problem, if this is occurring, is usually that a check valve (photo above-left) (found internal to some circulator pumps, or external as a physical device) intended to prevent hot water from circulating on its own - when the circulator pump is off - is either set to a "forced open" position, or it has become defective (less likely).
If that's the problem (diagnosed by a heating and service technician) then the valve or circulator needs to be replaced.
While waiting for that repair to be made, you can still turn off the heat when it is not needed, by turning off electrical power to the boiler.
The red Bell & Gossett B&G flo-control valves shown in our photo are designed to prevent hot water from circulating in a heating system unless the circulator pump is also running.
The valve provides a vertical-lift check valve function: until the circulator pump begins to run, the valve will prevent hot water from circulating through the piping system.
The B&G installation sketch (left, edited) shows a simplified but typical location of a flo-control valve - the red device at the right-most side of the sketch.
Which way do we turn the lever on a flo-control valve?
The lever on the top of the B&B flow control valves shown here allows the user or service technician to force the valve to an "open" position, overriding the valve's automatic internal operation. It's important that these B&G flo-controls are properly installed: the stem with the little lever needs to be upright. This flo-control valve is installed only in a vertical position, either at the top of a vertical pipe (where heat piping changes direction from vertical to horizontal) or in a horizontal heating pipe, but with the valve in an upright position. And the valve has to be installed with its flow-arrow pointing in the correct direction - in the direction off flow of heating water.
The valve handle is turned fully clockwise to prevent hot water circulation other than when the circulator is running. This is the normal setting for this control. When would we turn the lever counter-clockwise? We can think of several instances:
Emergency heat: the circulator pump is broken and we want hot water for heat to be able to circulate in the home by gravity until the circulator can be repaired or replaced - this is an "emergency heat" function that could be very useful. See Circulator Pumps & Relays.
Emergency heat: the building has lost electrical power and we want hot water for heat to be able to circulate in the building by gravity. Of course the length of time you'll have hot water for heat in the first place may be limited since the heating boiler's burner or safety controls will usually also be "off" if there is no electricity. But there are exceptions such as a combination wood-oil heating boiler system. See Wood Burning Heaters Fireplaces Stoves.
The heating system piping is air-bound and we are trying to force water through the system to flush out un-wanted air. See Air-bound radiators or piping. This feature is also used when the heating system piping is being filled with water after system drain-down or servicing.
Watch out: B&G warns users to remember to return the lever to the "closed" (fully clockwise) position after the emergency or service. Otherwise you'll get un-wanted hot water heat circulation by gravity even if the room circulator is not calling for heat. Also, these valves sometimes leak around the packing nut below the flo-control valve lever. The valve instruction and service manual describes how to remove, clean, and repair the valve without disassembling system piping.
At References we provide a link to an excellent resource to understand these flow control valves: the B&G Flo-Control Valves - installation, operation, and service instructions manual from Bell and Gossett - an ITT company.
B&G Hydrotrol™ Check Valves
Bell & Gossett (and other manufacturers) also provide a separate Hydrotrol™ valve to prevent hot water from circulating in a building by gravity when the room thermostat is not calling for heat.
This brass valve includes a knob that permits bypassing this check valve with a simple half-turn, achieving the same emergency heat or service functions we described above.
The Hydrotrol HT flow control valve - a specialty check valve e is used to prevent hot water from circulating through a building where the boiler is kept on to provide domestic hot water via a tankless coil or indirect water heater, during non-heating-season months.
It is also installed to prevent overheating of individual heating zones by gravity. But unlike the red B&G Flo-Control valves discussed above, the Hydrotrol flo-control valve can be installed both vertically and horizontally in heating piping.
Internal Flow Control Valves - IFC Valves on Heating Circulator Pumps
Check valves may be present on a hot water heating system (hydronic heating) but may be less easy to spot.
IFC valves or "internal flow control" check valves are built right into the circulator pump of some models, including some circulators made by Taco® such as the Taco nnn-IFC® (nnn=model number and IFC = internal flow control) circulator pumps.
Taco's product literature comments on the benefits of an IFC type circulator pump:
By locating the patented IFC® inside the pump casing, a separate in-line flow check
is eliminated, reducing installation costs. The reduced pressure drop of the IFC®, increases the
005 flow performance up to 240% over in-line check valves.
Reports are that failures of the check valve function in IFC type circulator pumps are rare.
Backflow Preventer Valves on Heating Boilers - A Different Check Valve
Backflow preventers are a different type of check valve found on heating systems.
The backflow preventer is installed to keep hot, high pressure water in the hydronic heating system from flowing backwards through a boiler water feed line into the building water supply - a sanitation concern.
Water Feeder Valves on Hot Water and Steam Heating Systems - as check valves
On older hydronic or steam heating boilers
the expansion tank and water feeder valve are separate physical units (photo at left). This automatic pressure-reducing water feeder combines a check valve and boiler water feeder. Like the separate backflow preventer described just above, the check-valve function, internal to the automatic water feeder device, prevents back-flow of heating system water into the building water supply piping.
This
bell-shaped device opens and sends makeup water into the heating boiler and its piping whenever the heating system's internal
water pressure falls below a normal level.
The feed-pressure i s typically factor-set to 12 psi when the boiler is cold, but adjustable where higher starting water pressure is needed for taller buildings.
Some older heating systems may not have an automatic
water feeder and may only provide a manually operated valve to add water to the boiler.
Systems without an automatic water feeder are
less safe and risk serious boiler damage should boiler water be lost and should there be no low water cutoff installed on the system. See WATER FEEDER VALVES for details about water feed valves for hydronic boilers. Steam boiler automatic water feed valves are discussed at Water Feeder Valves, Steam.
How to Identify, Reset, or Adjust Hot Air Heat Furnace Controls and Switches
For details about the setting, re-setting, or function of the controls and switches commonly found on hot air heating systems
see these articles:
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
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).
Questions & Answers regarding this article
Questions & answers about check valves and flow control valves on heating systems
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Additional technical contributors & reference sources for this article are listed below.
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Bell & Gossett Air Separators and other heating system components, Bell & Gossett, 8200 N. Austin Ave., Morton Grove IL 60053, USA - Tel 847 966-3700 Fax 847 965-8379. Air separators are discussed by B&G at http://www.bellgossett.com/homeowners/BG-airseparator.asp
Taco air scoops and other heating system components & controls: Taco Inc., 1160 Cranston Street, Cranston, RI 02920 / (401) 942-8000 / Fax (401) 942-2360 Taco (Canada) Ltd., 6180 Ordan Drive, Mississauga, Ontario L5T 2B3 / (905) 564-9422 / Fax (905) 564-9436 www.taco-hvac.com
Taco also has some helpful FAQs that are useful in diagnosing circulator problems - see http://www.taco-hvac.com/en/faq.html#
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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