Pressure Reducer Valves are used for boilers to decrease the pressure supplied to the boiler from the  make-up water feed. The make-up water feed originates from the city water source or well water source. The same water source you use for showering, washing dishes and sometimes drinking water depending on the quality. In many case, the pressure reducer valve or PRV is set to 12 PSI on most boilers. This is the pressure needed for many residential and commercial boiler water loops.

Pressure Reducer Valves and Make-up Water

Pressure Reducer Valves pressure reducer valve and backflow preventer

Pressure Reducer - Blue Arrow & Backflow Preventer - Red Arrow

In most cases, the make-up water supply is 40 or 50 psi and higher and this will exceed the safety rating of the lower pressure requirements of the boiler water loop. It will also exceed the pressure rating on the pressure relief valve on most residential boilers. For this reason, a PRV or pressure reducer valve is needed to decrease the pressure supplied to the boiler.

Pressure Reducer Valves for Hydronics - Finding the Valve

To find the PRV or pressure reducer valve simply follow the water source from the city water or well water supply. Follow it to the boiler. In many cases, it is half inch copper and sometimes 3/4 inch copper line which feeds the boiler water loop. You should see the PRV or pressure reducer valve in line with the back flow preventer. After the PRV it will feed into the boiler water loop usually near the expansion tank in many cases.

Both the PRV and the back flow preventer should have some sort of strainers inside of them and sometimes these strainers can get clogged up with trash so if your boiler is having a water feed problem check the strainers to make sure they are clean and so not have trash or debris clogging the strainers. If you are checking the strainers make sure you turn the water source off.

Pressure Reducer Valves - In the loop

In the photo above, the pressure reducer valve has a bypass lever on the top. This is typically used when filling the loop after initial installation or after a major loop repair such as replacing a circulator pump or other boiler water loop work. This lever should be closed when the boiler is in normal operation. If the lever is open then the pressure will be too high the pressure relief valve will likely vent and you will have a water spill to clean up. If you have pressure problems it is always good to check the pressure reducer valve to start.


In some cases, if it was installed by a good contractor you will pressure gauges on both sides of the pressure reducer valve so you determine absolutely that the proper pressure is being supplied to the boiler water loop. Other areas to when you have pressure problems or too high pressure are the boiler expansion tank. With a bladder type expansion tank you need to check to make sure it is properly pressurized with air and that the bladder inside the tank is not broken or busted. For steel type expansion tanks make sure the expansion tank is not over filled. A steel type expansion tank should be no more than 2/3rds to 3/4’s full to work properly.

For more information on hydronics click here.

High Performance

Pressure Reducer Valves for Hydronics

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