Originally Posted by tnthvac
It has been doing this since new, I have installed a pressure gauge on the spicket on the water heater and it varies from 55 psi water running and 120 psi after it sets for a while. What is the pressure relief set at on the valve, and could I have a bad pressure regulator on the main line? Thanks for your help!
The T&P ( the one that keeps opening) is normally set for 150 psi and 180 degrees F.
It sounds as though you have one of two problems. The expansion tank is bad, or undersized or... the pressure regulator (the one on the main, incoming line) is failing.
On the expansion tank, you'll find an air fitting, like on a bicycle tire. Let a touch of air out. Did you get water out?
If so, you have a bad expansion tank.
When hot water is heated, it wants to take up more room. The expansion tank is two tanks in one, separated by a flexible bladder. Air on one side, water on the other. The air will compress and give the expanding water someplace to go other than out the T&P. If that bladder has failed, then the tank is completely filled with water and the system has no room to expand, so it opens the T&P valve to 'relieve' itself.
Hope this helps.