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• Water feeder valves & pressure reducing valves on hydronic (hot water) heating boilers
• Automatic water feeder valves on boilers - adjust for building height
• What is the normal operating pressure of a hot water heating boiler? Heating Boiler pressure guidelines.
• What system pressure settings are needed for hot water heat
• When and how to add water to a hot water boiler

Here we discuss the various types of manual and automatic water feeder valves used on hot water heating boilers, including when and how to add makeup water to a boiler. A chart illustrates the adjustment to heating boiler operating pressure as a function of building height or the number of floors in a building being heated.

If radiators on the upper floors of your building are not getting hot, check that the heating system operating pressure is at the proper setting, and check that you radiators are not air-bound - see Air Bleeder Valves. Also be sure that your circulator pump and zone valves (if any) are working properly.

If your heating system uses a steam boiler, see Water Feeder Valves, Steam. If you don't know what kind of heat your building uses, see our introduction at BOILERS, HEATING. If your heating system is not working properly, see NO HEAT - BOILER / FURNACE DIAGNOSIS.This website answers nearly all questions about Heating System Boiler Controls on central heating systems to aid in troubleshooting, inspection, diagnosis, and repairs.

The photo above shows a modern automatic pressure-reducing water feeder valve on a hydronic (hot water) heating boiler - one of the safety controls which we discuss in this article. 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.

Hydronic (hot water) Heating Boiler Water Feed Valves

Manual water feeder valves on hot water boilers

Hydronic (hot water boilers) in proper condition do not normally consume any water. Once the boiler and the baseboard, radiator, or convector piping are connected and filled with water, that same water remains in the system indefinitely. The water in the boiler is heated and circulated through the occupied space to provide heat to the building occupants.

Water may be lost from a hot water heating system, however, due to a small leak that may be un-noticed, or water may be removed from the system during servicing.

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. To maintain the water level in these heating systems, water can be added from the building water supply piping manually by simply opening a make-up valve. A manual valve will simply be a shutoff valve that can be opened by hand to force water into the heating boiler.

Automatic water feeder valves on hot water boilers

On many heating boilers the expansion tank and water feeder valve are separate physical units.

On these older systems the "automatic water feeder" is often a bell-shaped device which 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 (perhaps 12 psi when the boiler is cold).

In our photo at left the gold colored bell-shaped device is an automatic pressure-reducing & water feed valve for a hot water boiler. An arrow on the valve base shows the direction of water flow (from building supply at right into the boiler at left).

The screw and lock nut on top of this valve permit adjustment of the automatic water feeder valve pressure (it's normally set to 12 psi).

The horizontal lever is a bypass that will send water through the valve on to the boiler at full building pressure (it's normally left "off" in the position shown here).

The device to the right of the automatic water feed valve is a back-flow preventer that is required in some municipalities. The back-flow preventer makes sure that water from inside the heating boiler cannot flow backwards into the building (and community) water supply. This prevents back-contamination of potable water piping from the boiler should the building water pressure fail.

An automatic water feeder used on hot water heating boilers performs two functions:

1. The automatic water feed valve reduces the incoming water pressure from the building supply side down to (typically) 12 psi. That's because the normal in-boiler water pressure, when the heating boiler is cold, is about 12 psi in a normal residential system. A tall building may need to start with higher cold-system water pressure to be able to push hot heating water to upper floors.
   
   
2. The water feed valve adds water to the boiler when needed: If water pressure in the heating boiler drops below 12 psi, the water feeder valve will add makeup water to the system automatically, until it reaches 12 psi inside the boiler.

The automatic water feeder has two additional features:

1. Valve override: Lifting the lever over the valve body (B&G valve shown at page top) will overcome the 12-psi feature and force water into the heating boiler at building pressure. This feature is not normally used, but it's useful during some service procedures such as refilling a boiler that has been drained (more rapidly than otherwise) or for temporarily forcing water into a heating boiler at high pressure for diagnostic reasons or to attempt to force air out of an air-bound hot water heating system.
   
   
2. Valve pressure adjustment: The incoming water pressure setting of 12 psi can be adjusted up or down by the service technician.
   
   The red Armstrong™ pressure reducing valve shown here includes a black plastic cap covering its adjustment screw under the black plastic cap on top of the valve.
   
   You'll see a similar screw (and lock nut) on the B&G water feeder valve in the photos above on this page.

Photo Guide to Heating Boiler Pressure Reducing Valves

Our photo at above left shows an Armstrong™ pressure reducing valve. The schematic at above right, courtesy of Carson Dunlop, explains how this pressure reducing valve works.

Safety note: If the pressure reducing valve is combined with a pressure relief valve, for safety these parts must be installed in the correct position. As Carson Dunlop shows in this sketch, the pressure relief valve should always be installed closest to the heating boiler so that it can respond to an overpressure in the heating system.

What is the proper water pressure setting for a pressure-reducing valve or water feeder valve on a Hot Water Heating System?

What is the normal operating pressure of a hot water heating system boiler?

Hydronic heating systems (hot water) typically operate at about 12 psi cold and see a pressure increase to somewhere just under 30 psi when the system is at maximum temperature.

If you set the water feeder pressure too high it's likely that when the boiler heats-up to operating temperature, the water pressure will exceed the safety limit (30 psi) and the boiler relief valve will open to discharge excess pressure and water.

Because a hydronic heating system's circulator pump has little "lift" capacity (it just pushes the water around the loop of boiler and heating piping and radiators), the heating system depends on its internal water pressure to lift hot water to radiators (baseboards, or convectors) on upper floors in the building.

A higher building may therefore need higher heating system water pressure in order to be able to circulate heat adequately to upper floors. The sketch, courtesy of Carson Dunlop, explains that a three-story building will need heating system pressure set up to at least 15 psi. when the heating boiler is cold.

But in most cases you should leave the water feeder at the psi set by the installer (typical factory setting is 12 psi) unless the building has unusual conditions (such as more than two stories) that require a higher in-boiler starting water pressure.

Automatic Water Feeders Built-Into Expansion Tanks

An automatic water feeder valve is included as part of some heating system expansion tanks on hydronic heating boilers - in a single unit such as those provided by Amtrol™, Extrol™, Fill-Trol™, or similar expansion tanks.

The water feeder is the brass assembly found attached to the expansion tank where piping from the boiler enters the tank on these units.

In our photo at left you can see the brass valve on top of the Fill-Trol™ expansion tank and underneath the cast iron air purge valve.

The vertical copper pipe is feeding water from the building supply, at building water pressure into the brass valve and through it, upwards into the heating system distribution piping through the silver painted cast iron air purge valve.

This automatic water fill valve is not adjustable by the consumer and is factory-set.

Steam Boiler Water Feeder Valves, Automatic & Manual

Keeping the proper amount of water in a steam boiler is a critical function for both safety and to avoid damaging the boiler itself. So on a steam boiler we consider the automatic water feeder to serve as a safety device too. Water feed valves on steam heat systems operate under very different requirements than those on hot water (hydronic) heating systems.

Residential steam heating systems are mostly "low pressure" systems operating at less than 2 psi. In fact if you see the pressure set higher on a residential system it is often an indicator that the occupants/technician have been having trouble getting the steam heat to locations where it's needed.

But steam heat systems all consume some water which escapes from radiator air vents during the time that the steam (heat) is first rising in the building. So unlike a hydronic water feeder, the steam boiler water feeder is going to be much busier, regularly adding makeup water to the steam boiler, but operating at low water pressures.

Automatic water feeder valves on steam boilers

Automatic water feed valves on steam boilers (such as the McDonnell & Miller automatic water feeder shown at left) perform functions similar to the valve described earlier for hot water boilers.

But because the steam boiler will be damaged or unsafe if its water level falls too low and because it's normal for a steam system to use (lose) water, the water feed valve on a steam boiler has to operate more often, and will be a more heavy-duty (and probably reliable) device.

The black box shown in our photo at left is a Mcdonnell & Miller™ automatic water feed valve. On a signal (normally from the low water cutoff valve) the water feed valve will open to send additional makeup water into the steam boiler.

Manual water feeder valves on steam boilers

In our photo at automatic water feed valves, an automatic water feeder is installed (the black box discussed below). But the yellow handle is an manual water feeder that will bypass the automatic water feeder and force water into the boiler. On this particular system you shouldn't need to use the manual feeder lever unless the automatic feed valve is broken.

As you see, the yellow handle is in the horizontal position, "across" the water pipe, showing that it is in the "closed" position (we're depending on the automatic feed valve).

But on lots of steam boilers, especially older residential units, you may find that only a manual feeder valve is installed. You'll need to use it whenever the steam boiler water level is low (discussed below).

How often you'll need to manually add water to a steam boiler that lacks an automatic feeder depends on how rapidly your particular steam heating system loses water. If you are new to your particular steam heat system, you should check it's water level (and flush the low water cutoff valve) at least weekly until you know more accurately how the heating system behaves in normal use.

Steam heating 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. That's why all modern steam heating boilers can be expected to include at least a low water cutoff valve. Low water cutoff valves are discussed in detail at Low Water Cutoff Valves, Boilers.

How Much Water Should Be Added to a Steam Boiler

If your steam boiler has an automatic water feeder you should see the water level always close to the fill-mark and the automatic water makeup valve will normally do this job for you.

If your steam boiler has only a manual valve for adding water, until you know the system's rate of water usage, you should check the water level at least once a week during the heating season.

You'll want to add water whenever the sight glass shows that the water level has dropped to the "add" mark and you should always see some water in the sight glass.

The sight glass on a steam boiler, combined with a mark or gauge usually placed on the sight glass or on the boiler body behind the glass, will show the proper level to which the steam boiler should be re-filled when it's low on water.

See Sight Glass, Steam Boiler for details of this component.

Our discussion of radiators or baseboards that do not get hog when they should includes these key sections:

1. Air Bleeder Valves - a Guide to Air Bleeder Valves for Hot Water Heating Systems: Radiators, Baseboards, Convectors - how to find and use manual and automatic air bleeders to fix noisy gurgling heating pipes or an airbound heating system. Air purges for steam heating systems are discussed separately at Steam Vents.
2. Airbound Heating System Relief Procedure #1 Using Water Feeder & Boiler Drain - how to use built-in controls and valves to force air out an air-bound heating system whose radiators, convectors, or baseboards are not warming up
3. Airbound Heating System Relief Procedure #2 Using a Pony Pump - how to use a portable pump, short sections of garden hose, and heating system valves to force air out an air-bound heating system whose radiators, convectors, or baseboards are not warming up.
4. Water Feeder Valves, Hydronic - a defective automatic water feeder valve on a hot water heating boiler can result in too little starting water pressure in the system - radiators on upper floors may fail to receive heat. On a steam heating boiler a defective automatic water feed valve can cause the heating system to shut down completely or can lead to boiler damage or even unsafe conditions. At Boiler Pressure Settings we discuss the pressures needed for hydronic or hot water heating systems - a taller building needs higher starting (cold) pressure in the heating boiler. At Water Feeder Valves, Hydronic we discuss problems with water feeder valves that also control water pressure in the boiler and we explain how to adjust the water feeder valve and thus boiler water pressure. If your heating system uses a steam boiler, see Water Feeder Valves, Steam.

Readers should also see Diagnose Oil Heat Noises for diagnosis and repair of other heating system noises on both oil and gas fired heating equipment. This website answers most questions about central heating system 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.

If you don't know what kind of heat your building uses, see our introduction at BOILERS, HEATING. If your heating system is not working properly, see NO HEAT - BOILER / FURNACE DIAGNOSIS.This website answers nearly all questions about Heating System Boiler Controls on central heating systems to aid in troubleshooting, inspection, diagnosis, and repairs.

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• Thanks to Alan Carson and Bob Dunlop, Carson Dunlop, Associates, Toronto, for permission to use illustrations from their publication, The Illustrated Home which illustrates construction details and building components. Carson Dunlop provides home inspection education, publications, report writing materials, and home inspection services. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.

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More Information on Building Diagnostic Inspections and Repairs

• Carbon Dioxide Gas Toxicity
• Carbon Monoxide Gas Toxicity, exposure limits, poisoning symptoms, and inspecting buildings for CO hazards
• Dust from HVAC? An Investigation of Indoor Dust Debris Blamed on a Heating/Cooling System Reveals Carpet Dust
• Goodman Furnace High Temperature Plastic Vent HTPV safety recall US CPSC notice
• Home Heating System Should Be Checked [for proper venting and for CO Carbon Monoxide Hazards - DJF]
• Inspection Procedures for Oil-Fired Heating Systems Detailed step by step approaches for inspecting complex systems]
• Lennox Pulse Furnace Safety Inspection/Warranty Program: Carbon Monoxide Warning
• Oil Tanks - The Oil Storage Tank Information Website: Buried or Above Ground Oil Tank Inspection, Testing, Cleanup, Abandonment of Oil Tanks
• Oil Tanks Above Ground, UL Standards, guidance for home owners, buyers, and inspectors
• Plastic Heating Vent Pipe & Other Heating Safety Recall Notices
• 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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