LARGER VIEW of a heating boiler cad cell relay switchWater Feeders, Pressure Reducing Valves on Hot Water (Hydronic) Heating Boilers
Automatic boiler water feeder valves

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Heating boiler pressure reducer valves - sometimes mis-named as boiler water feeder valves:

Here we explain hot water boiler (hydronic heat) pressure reducing valves and 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.

We include photographs of common pressure reducer valves and water feeders used on hot water heating boilers to aid in product identification, links to installation manuals, safety warnings, installation and pressure reducer / water feeder safety and maintenance tips.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Hydronic (hot water) Heating Boiler Water Feed Valves

BandG Pressure Reducing Valve (C) Bell & Gossett ITTThe 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.

[Click to enlarge any image]

Article Series Contents

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

Automatic water feeder for hot water boiler 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 pointed to by the red arrow is an automatic pressure-reducing & water feed valve for a hot water boiler.

An arrow cast into the valve base shows the direction of water flow (from building supply at right into the boiler at left in this photo).

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 separate heating system backflow preventer / check valve indicated by our green arrow in the photo above is discussed in more detail


Automatic Heating System Automatic Water Feeder Includes Built-In Backflow Preventer

The device to the right of the automatic pressure reducer (water feed valve) in our photo above 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.

See CHECK VALVES, HEATING SYSTEM for more information about backflow preventers and other heating system check valves.

BandG Reducing Valve (C) Bell and GossettAn automatic water feeder used on hot water heating boilers performs two functions:

Bell & Gossett's sketch of their pressure reducing valve is shown at left.

  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.

    [click to enlarge any image]

  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.

So is the B&G Pressure Reducer an Automatic Water Feed Valve or Not?

Well yes, and no. The valve can automatically feed water into a hot water heating boiler whose pressure falls below the set-pressure (12 psi at factory setting) if the water shutoff valve for the boiler has been left "on".

BandG Pressure Reducing Valve (C) Bell & Gossett ITTThe B&G pressure reducing valve shown at left includes a bypass lever shown in the "up" or "open" position in the illustration. In this position water is fed into the boiler at street pressure.

When the valve is "down" in the "closed" position, IF the shutoff valve before the pressure reducer is open, water is fed to the boiler if its pressure drops below the valve's pressure setting (adjusted by the lock-nut and screw on the valve top).

But the manufacturer warns that the purpose of the pressure-reducing (and automagic water feeding) valve is to fill heating boilers after installation or servicing. The company says

"It is not a safety device and is not intended to be used as as a water feed valve to control boiler water at a safe operating level".

OPINION: this is interesting since for closed-system hydronic heating boilers (not steam boilers) that's how lots of service techs and inspectors view this device.

In the company's service manual you'll see on the installation piping sketch (edited) for the pressure reducing valve (green, to the right of the blue shutoff valve at the left side of the sketch below) that they expect the installer to include a water shutoff valve (blue at the left end of the sketch below) before this pressure reducer.

Keep the manual water feed shutoff valve closed?

B&G wants you to keep the boiler water supply valve shut except during service - as a precaution that allows easy detection of a boiler leak by noticing the reduced water pressure in that system.

The company also points out that too-frequent feeding of water into a heating system can increase the effects of corrosion and system damage.

In my [DF] opinion, a typical building owner or occupant almost never thinks to check the water level in a hydronic heating system (hot water boiler) until there is some indication of a problem (like no heat or a damaged leaky boiler).

Heating control installation sketch BandG (C)ITT B&G modified by DJFIn our experience most hydronic heating boiler installers and service techs leave that shutoff valve "open" or "on" so that the boiler won't be at risk of being ruined or unsafe by operating at low or no-water level - their experience may be similar to mine.

The manufacturer is telling you what's safe in some regards, but they may not have the same view of what people actually do in the field.

Add a low water cutoff safety valve

A safety improvement on hydronic boilers that gets around this argument is to add a low-water cutoff on residential hydronic heating boilers (hot water heating boilers).

That device, always present on steam boilers, is required by local codes in some jurisdictions for hydronic heating boilers too.

OPINION: on a hot water heating boiler that does not have a low-water cutoff valve installed, we would be reluctant to leave the building unattended for weeks or months during the heating season with the boiler water supply shutoff valve in the closed position.

We would think about leaving the water supply valve open - not what B&G recommends. That way if a small leak develops we're not at risk of destroying the boiler by firing it without adequate water in the system.

This violates the B&G installation instructions for their pressure reducing valve - so be sure to review this concern with your trained, heating service company service manager.

Differences in Makeup Water Requirements - Hydronic Heat versus Steam Heating Boilers

In normal use, a hydronic or hot water heating system does not consume any water. Only if there is a leak (or during service) would the water level in a hot water heating system drop and need replenishment.

That is an abnormal condition, and one that means the system needs to be repaired.

Keep in mind that devices like the B&G Pressure Reducer (notice they don't call it a "water feeder" even though it feeds water to the boiler) is intended for hot water or hydronic heating boilers.

But a hot water heating system might have a tiny, small, even hard-to-find water leak that goes un-noticed for some time, especially if the boiler water supply valve is kept open so that the pressure valve also feeds a little makeup water into the boiler when needed.

Conversely, on a steam heating system the boiler is expected to consume water at every operating cycle - the feed frequency is therefore much greater on a steam boiler and this B&G pressure reducer/water feeder would not be the proper device to use for water feeding.

For water feeders used on steam boilers,


The Pressure Reducing Valve (automatic water feeder) has two additional features:

Faulty pressure reducer valve (C) Daniel Friedman
  1. Pressure Reducing 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.

    Watch out
    : forcing cold water into a hot heating boiler can cause it to crack or be ruined.

    Keep this "shutoff valve" or override lever closed except during initial filling of the boiler or when manually adding fill to a cool or cold boiler as part of service.

    Installing the proper automatic pressure reducer water feeder should prevent this problem by feeding water to the boiler before boiler water pressure (or level if proper controls are added) is too low, and at a slow enough rate.

    As B&G puts it NEVER ADD WATER TO AN OVERHEATED BOILER. Failure to follow those instructions could result in serious personal injury or death and property damage.

    Watch out: constant addition of fresh makeup water to a heating boiler that is leaking can make discovery of the leak more difficult, and by constantly introducing fresh water, can lead to mineral deposits, clogging, or boiler damage.

    Watch out: take a look at the funny lever position on the pressure reducing valve in our photo (above-left). Is it closed, off-bypass (down) or is it partly open (up)? We weren't sure, but this very valve was blamed for a major house flood causing thousands of dollars in damage from mold.

    The building was unattended and the valve fed water into the structure for days, resulting in flooding and mold contamination. We wondered if the house-watcher made a mistake or was messing around with this device before the flood.

    Watch out: yep one more. The manufacturer warns that

    The Bell & Gossett Pressure Reducing Valve is designed for filling hot water boilers and associated piping systems to a properly controlled pressure after boiler installation or system servicing.

    It is not a safety device and is not intended to be used as a water feed valve to control boiler water at a safe operating level.

    They are factory set at specified limits although adjustment is easily made. They are equipped with a built-in strainer and low inlet pressure check valve.

  2. Pressure Reducing Valve Set-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.

    Loosening the lock nut and then turning the screw on the top of the pressure-reducing valve "in" or "clockwise" increases the set pressure of the control. See B&G's "Reducing Valves Installation, Operation, & Service Instructions" linked-to

    at REFERENCES below.

Photo Guide to Heating Boiler Pressure Reducing Valves

Water feeder valve for a hot water boiler Schematic of pressure reducing valve

[Click to enlarge any image]

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

Pressure reducer water feed valve on Energy Kinetics boiler (C) Daniel Friedman


Our photo (left) shows another model of pressure reducer valve on the water supply line to an Energy Kinetics oil fired heating boiler.

The lever on the top of this valve combines a full-open bypass (when the lever is vertical) and a set-pressure adjusting locknut (below the round lever body).

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 Associates shows in the sketch above,

and as you'll also see in the B&G installation piping 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?

Heating system pressure requirements to get heat to upper floorsWhat 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.

[click to enlarge this or any image]

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 Associates, 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

Expansion tank with fill valveAn 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 (red arrow).

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 to add water to the heating boiler whenever the system pressure falls below 12 psi.

The tank below the red arrow is, of course, an expansion tank. We discuss expansion tanks and their troubleshooting or maintenance


Steam Boiler Water Feeder Valves, Automatic & Manual

Steam boiler water feederDetails about automatic water feeders for steam heating boilers are

at WATER FEEDER VALVE, STEAM. Excerpts are just below.

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.

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.

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.

All 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.

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


Pressure Reducing Valve Troubleshooting, Inspection, Service & Repair Procedures

Clogged pressure reducer valve won't feed water to the boiler B&G B-8 (C) Daniel Friedman at InspectApedia.comInspect & Check the Pressure Reducer for Proper Operation, Clean the Strainer if Needed

B&G offers some excellent tips on how to check the pressure reducer for proper operation, and how to fix some common problems.

Clogged pressure reducer valve won't feed water to the boiler B&G B-8 (C) Daniel Friedman at

Clogged pressure reducer valve won't feed water to the boiler B&G B-8 (C) Daniel Friedman at

Water Pressure-Reducing Feed Valve Inspection Tips

Water Feed Valve - ASHI InspectorReader Question: What should we report if finding a water feed valve tied off as shown in this photo?

Tom Sherman - President, Absolute Home Inspection, Inc., 315-673-1755 provided this photo of a tied-off pressure-reducer water-feed valve and asked what we'd say about it, for an ASHI home inspector newsletter.

Home inspectors are expected to be competent to recognize conditions at a home that are improper, unsafe, not functional, etc. provided that the problem or component is readily accessible, visible, and under some other conditions.

In this photo we have a pressure-reducing water feed valve typically used on a hot water or hydronic heating system.

The valve valve, this one is a B&G model, has the job of feeding makeup water to the heating boiler should the water pressure in the heating system fall below the set-pressure on the valve - typically 12 psi for most one or two story residential buildings, though the set pressure may need to be higher in taller structures.

The water feed valve's override lever in the photo has been secured to the water pipe by a black plastic tie.

The override lever is used to put the water feed valve into "bypass mode" by lifting the lever to a 90-degree position above the water piping and valve body - meaning that the valve is manually forced "open" to allow water to enter the heating boiler at whatever pressure is on the inlet side of the valve.

(The heating boiler, not shown here, is always on the outlet side of the valve, and on most of these controls an arrow cast into the valve body indicates the intended direction of water flow.

In our photo we've drawn a blue arrow showing the direction of water flow for this valve. Click the image to see an enlarged version.

If the valve were in manual OPEN mode, the lever would be at right angles to the piping and valve body - its handle would be over the adjustment screw shown in the center of the valve top. So this valve is in the CLOSED position.

Why would someone put a plastic tie on the automatic water feed valve override lever to hold it in the CLOSED position?

Perhaps the heating service technician was annoyed by an owner's emergency service call complaining that the pressure / temperature relief valve was spilling and perhaps the tech found that the owner had been messing with the valve and over-pressurizing the boiler. If you set the boiler water pressure too high when cold then when the boiler heats up the pressure will exceed the (roughly 30 psi) pressure at which the relief valve will open.

But a more likely reason this valve was tied OFF or CLOSED was that it was leaking, feeding excess water pressure to the boiler on its own. One of the failure modes of these valves is that the valve begins to feed water when it should not. That can happen due to dirt and debris in the valve or for other reasons. Someone was trying to force the valve to behave itself.

Functional & Safety Worries with a Bad Behaving Water Feed Valve

Watch out: this is not only an improper heating system operating setup, it is potentially (though subtly) quite dangerous:

Watch out: The manufacturers of this type of automagic water feed valve recommend that additional manual control valves be included in the piping system, so in some installations you might also find that the automatic water feeder is not really so automatic.

... the manufacturer warns that the purpose of the pressure-reducing (and automagic water feeding) valve is to fill heating boilers after installation or servicing. The company says

"It is not a safety device and is not intended to be used as as a water feed valve to control boiler water at a safe operating level".

Which is pretty interesting since so many people in the trades as well as among inspectors consider it a safety device.

This article series answers nearly all questions about Heating System Boiler Controls on central heating systems to aid in troubleshooting, inspection, diagnosis, and repairs.

How to Install an Automatic Pressure Reducing Valve / "Water Feeder"

The discussion of how to install a pressure reducer / water feeder has moved


The discussion of how to fix a clogged pressure reducing valve has moved



Continue reading at CHECK VALVES, HEATING SYSTEM or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see WATER FEEDER VALVE / PRESSURE-REDUCER FAQs - questions posted originally at this page


Or see PRESSURE REDUCING VALVE DISASSEMBLY - internal parts, what clogs.


Or see WATER FEEDER VALVE, STEAM If your heating system uses a steam boiler

Or see this

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Suggested citation for this web page

PRESSURE REDUCING VALVES at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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