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Rick
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Category: HVAC
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Experience:  40+ yrs. experience as a licensed oil & gas technician.
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My furnace keeps going above 30 psi, causing the relief valve

Customer Question

My furnace keeps going above 30 psi, causing the relief valve to open. Supply pressure valve seems to be in good condition. Pressure at rest is 12 psi. Disconnected line to expansion tank, no water comes out, tank sounds hollow. Any suggestions?
Submitted: 4 years ago.
Category: HVAC
Expert:  Rick replied 4 years ago.
Chat Conversation Started
Rickheatdoc :

Welcome to Just Answer, I will do my best to help you solve your problem

Rickheatdoc :

If the pressure rises as the temp rises to the point where the relief valve leaks then you have an expansion problem. The tank could be too small or may have failed

Rickheatdoc :

If you have an old style expansion tank (usually between the floor joists ) then you could try draining the tank or installing a new diaphragm type

Customer :

yeah a problem with the tank was my guess too. Is there anyway to test it?

Rickheatdoc :

Which type do you have

Rickheatdoc :

old style or diaphragm

Customer :

its is an old looking vertical cylinder about 10" wide and 18" high

Customer :

old style I'm sure

Rickheatdoc :

If it doesn't have a fitting to let air into the tank then you won't get water out of it with a hose attached. The only way to drain it is into a bucket.

Rickheatdoc :

It will take quite a while as air gets sucked into the tank as it's draining

Rickheatdoc :

So you either drain all the water out of the old tank then re-open the valve to the system SLOWLY. or you replce the tank with a modern one

Customer :

sounds like I'd be better off with a modern one

Customer :

any suggestions on size of tank needed for a 93000 btu/hr output furnace?

Rickheatdoc :

If you have copper baseboard or convectors you would use a #30. If you have cast iron baseboard or radiators then you need a #60

Indeed. You can tie it into the same line as the old tank unless you have an air scoop on the heating main with a 1/2" female tapping in the bottom. If so then you could just screw it into this tapping.

Customer :

okay, I'll go ahead and get one tomorrow. Thanks for the help.

Rickheatdoc :

Please hit accept
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