PRV Question - Posted in wrong forum initially

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Jdjd

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Any feedback on my inquiry below that was posted in the wrong forum?

My initial question:


My pressure relief valve has started to leak. I'm 95% sure it is the expansion tank that is full of water, but would like to rule out the pressure reducing valve. How can I test the pressure reducing valve?

Response 1:

First, if the PRV is leaking, rebuild, or replace it! Second, if the expansion tank is waterlogged, same thing...replace it. The only way to check a PRV for proper action is to have a pressure gauge installed and monitor it under various conditions. IF your ET is working, the pressure should remain where you've set the PRV. IF it gradually goes up or never is reduced and the WH is not running, the PRV is bad.

My reply:

Yes, I plan to replace both the relief valve and expansion tank. Would I install a pressure gauge on one of the boiler drains?

Respose 2:

You'd need to find somewhere else to attach a pressure gauge...the boiler SHOULD be at much less pressure than the domestic supply (typically 12-16#). A washing machine supply, or the drain on the WH, or an outside hose bib, or nearly anywhere with an adapter. Or, if you want it more permanent, you could get one with a NPT on it, and install a threaded T somewhere after the PRV and screw one in permanently. Or, if you're really interested, install two, one before and one after the PRV.

My reply:

I've been googling this topic today. I found the following:

To test a PRV, shut off water supply, drain water to drop boiler pressure, turn on water, watch the pressure gauge for a few hours while not firing boiler. If pressure does not rise, or continues to rise past the set point, then replace the PRV.

Your thoughts on this?

Reply 3:

Most PRVs are for the incoming city water. Initially the supposition was that is what you were asking about.

Had you posted in the Boiler Forum, then it would have been assumed that you were talking about some part in your hydronic heating system. It now appears that you are talking about a part of your hydronic heating system.
 

Jadnashua

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There are three general reasons why water in a boiler increases:
1. The expansion tank is shot leaving no space for the heated water to expand which causes pressure to rise, usually causing the safety relief valve to open to relieve it. When the boiler turns off, the pressure drops a bit, and the autofill may open, filling the system and opening it up for the same cycle over and over again as the boiler heats then cools off.
2. The auto fill valve is leaking, letting the potable water supply to feed water in when not needed.
3. A variation on #2...a small leak in an indirect water heater coil allowing potable water pressure to fill the hydronic system (this one can be a health issue).
 
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