Guide to Heating System Boiler Check Valves, Flow Control Valves, Backflow Preventers

CHECK VALVES, HEATING SYSTEM - Troubleshooting heating system check valves, flow control valves, flo-control valves, backflow valves used on heating equipmnent
- What are flow-control valves & how do they work?
- What are IFC circulators - internal flow control valves?
- BACKFLOW PREVENTER VALVE, HEATING SYS
- How do automatic water feed valves also function as a check valve on heating systems?
- Cleaning & maintenance guide for heating systems
BACKFLOW PREVENTER VALVE, HEATING SYS - separate valve prevents back-contamination of building water supply piping from heaters
BACKFLOW PREVENTER, HEATER WATER FEEDER - to prevent back-contamination of building water piping thorugh water feeder
BACKWATER VALVES, SEWER LINE - check valve in sewer line prevents building flooding
CHECK VALVES, WATER SUPPLY - on water supply piping to prevent backflow or loss of well prime
FOOT VALVES, WELL PIPING - check valve in the well to prevent loss of pump prime
PLUMBING CONTROLS & VALVES - home
SEWAGE PUMPS - check valves in sewage ejector pumps
Questions & Answers about check valves and flow control valves on heating systems
References

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This article explains types of check valves used on hot water 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. This website answers most questions about Heating System Boiler Controls on central heating systems to aid in troubleshooting, inspection, diagnosis, and repairs. If you are looking for information on water supply piping & well system check valves see WATER SUPPLY SYSTEM CHECK VALVES.

Check Valves on Hot Water Hydronic Heating Systems - Flow Control, Flo-Control Valves, Inspection, Settings, Problems

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.

Because on some hot water heating systems the check valve or flow-control valve is integrated into the circulator pump assembly, also see Circulator Pumps & Relays.

For an example of how the check valve or flo-control valve functions on hot water heating systems, and what goes wrong, also see Heat Won't Turn Off - Stop Unwanted Heat. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.

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 Lower 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 below the current room temperature, the heating system (hot water or steam) boiler or (warm air) furnace should not run.[1]

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.

[Warm water is less dense than cold water and will rise up through cooler water, displacing it and sending cooler water down to the boiler.]

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. With the heating boiler switched off it will cool down and water will stop heating the radiators by gravity or convection circulation.

Heating control installation sketch BandG (C)ITT B&G modified by DJF

The red Bell & Gossett B&G flo-control valves shown in our photo above and in the sketch at left 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 System Piping - A Different Check Valve

Heating System Backflow Preventer Valves Protect Public Water Mains / Private Water Piping from Heating System Water Contaminants

Automatic water feeder for hot water boiler

Because a building potable water supply piping cold water line is used to deliver water to hydronic or steam heating boilers, we need to prevent heating system water from back-contaminating the building water supply piping. At a hot water heating system a heating system backflow preventer check valve is used 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.

On both hot water (hydronic) and steam heating systems the backflow preventer may be built into the automatic water feed valve (photo at left, also see BACKFLOW PREVENTER, HEATER WATER FEEDER).

At our heater backflow photo (above left) the automatic water feed valve (red arrow) includes a built-in backflow prevention device.

Depending on local plumbing codes, a separate (from the water feeder valve) dedicated backflow preventer valve may also be installed "upstream" of the automatic water feeder - that is, between the heating system water feed valve and the incoming municipal water supply cold water piping (green arrow). A closeup of the separate heating backflow preventer is shown in a second photograph below.

These are two separate devices for heating system water backflow prevention, but often you will see both of them installed.

The blue arrow in our photograph shows the direction of water flow into the water feeder and onwards into the heating boiler.

In sum, backflow preventers found on heating systems are installed to prevent higher-pressure heating system water from being forced backwards (say through a water feeder valve) into the building potable water supply piping.

Details about automatic water feeders are at WATER FEEDER Valves, Hydronic and WATER FEEDER Valves, Steam.

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

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).

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Technical Reviewers & References

Related Topics, found near the top of this page suggest articles closely related to this one.

[1] Thanks to reader WJP for careful editing and reading about the relationship between room temperature and thermostat settings 1/1/2012
[2] "Water Circulation Pumps & Circulators", TACO (PDF)
[3] B&G Flo-Control Valves - installation, operation, and service instructions manual - original source Bell & Gossett, 8200 N. Austin Ave., Morton Grove IL 60053, USA - Tel 847 966-3700 Fax 847 965-8379 . www.bellgossett.com/BG-Literature-Detail.asp?LiteratureID=607
[4] 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
[5] 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#
[6] Domestic and Commercial Oil Burners, Charles H. Burkhardt, McGraw Hill Book Company, New York 3rd Ed 1969.
[7] 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.
[8] 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,
[9] Principles of Steam Heating, $13.25 includes postage. Fuel oil & Oil Heat Magazine, 389 Passaic Ave., Fairfield, NJ 07004.
[10] The Lost Art of Steam Heating, Dan Holohan, 516-579-3046 FAX
[11] 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).
[12] "Residential Steam Heating Systems", Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
[13] "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
[14] "Warm Air Heating Systems". Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
[15] Heating, Ventilating, and Air Conditioning Volume I, Heating Fundamentals,
[16] 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
[17] Installation Guide for Residential Hydronic Heating Systems
[18] Installation Guide #200, The Hydronics Institute, 35 Russo Place, Berkeley Heights, NJ 07922
[19] 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.)
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides:
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  Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
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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, 25th Ed., 2012, 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. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.

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Building inspection education & report writing systems from Carson, Dunlop & Associates Ltd

Carson Dunlop, Associates, Toronto, have provided us with (and we recommend) Carson Dunlop Weldon & Associates' Technical Reference Guide to manufacturer's model and serial number information for heating and cooling equipment
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
"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
Installation Guide for Residential Hydronic Heating Systems
Installation Guide #200, The Hydronics Institute, 35 Russo Place, Berkeley Heights, NJ 07922
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