Furnace Pressure Relief Valve dripping

Static pressure of the system is the pressure at the tank with all pumps off. No valves closed. The settings value of pressure you need you will get by calculations. It is the height of the heating system in FT, divided to 2.431 and to resulted value add 5\. This will be pressure setting of your feed valve, and air pressure in expansion tank, when tank disconnected from heating system and has no water pressure on water side of diaphragm. When all will be set, your relieve valve will no longer have a reason to open up.

ellenlourie

in Heating and Cooling 10 years and 6 months ago

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zhideng | 10 years and 6 months ago

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The pressure relief valve on my furnace seems to get a slow leak when the heat is on. It’s very little but over the course of the time when the heat is on the small bucket I have below collects a little bit of water. This has not happened in the past and I think I need to replace that valve. I called one heating person and they quoted me 350 to replace it because I have to drain the whole system, replace it then bleed each radiator(hot water system). Is that a fair price for that type of work? We checked all the other components of the system and it seems to just come down to a leaky relief valve. Any recommendations on another heating person that might be able to give me a second opinion?

thetinkerswagon | 10 years and 6 months ago

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not sure about having to drain the entire system, but 350 for a plumber to do anything sounds reasonable. also, that includes the valve? that must be a 60 to 80 dollar item itself.

ellenlourie | 10 years and 6 months ago

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Your expansion tank is broken. Get a new one.

eman134 | 10 years and 6 months ago

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Like gennady said, a dripping pressure relief valve is symptomatic of other problems, most likely a blown expansion tank, which may well have been undersized to begin with. Replacing the prv will not solve the underlying problem

zhideng | 10 years and 6 months ago

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I knocked on the expansion tank and one side is solid while the other hollow. I know that its not a fullproof way to test if its working but how would the expansion tank cause the relief valve to leak? Wouldn’t it prevent water from coming into the system via the pressure reducing valve? I am not an expert but just piecing together what I learned via the internet. I was also thinking it might be the pressure reducing valve letting too much water into the system as the pressure gauge reads just above 25lbs which seems kind of high. I know that gauge might not be terribly reliable but it should be close ballpark figure and maybe is the reason the relief valve is leaking because the pressure is probably at around 30lbs which is what its rated for.

ellenlourie | 10 years and 6 months ago

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The purpose of expansion tank is a compensation of thermal expansion of the water. if expansion tank not working, water has no room to expand, pressure rises and relive valve does what it is installed for, opens up and relieves excessive water to keep pressure under setpoint. Expansion tank must be pumped to pressure equal necessary static pressure of the system plus 5 PSI, and pressure in the tank must be checked at least once a year with tank disconnected from the system during maintenance visit. Usually tank loses 2-3 PSI a year.

zhideng | 10 years and 6 months ago

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Ok so if i measure the psi from an drain outlet and then pump the expansion tank to that value +5 that should correct the leak? Do I need to close any of the valves from the water feed or return feed from radiators?