pt valve leaking on hot water tank

The pressure/temp valve on my hotwater tank is leaking so I have replaced it along with my vacuum relief. the valve continues to leak so I had put a pressure gauge on my outdoor hose bib and found it had spiked to 150psi so i changed out my prv my house is 50 plus years old and figured that had to be the problem. Check the pail under my P/T valve and it has water in it again. What is causing it to open.


PT

have you addressed thermal expansion in any way? And wow..150psi house pressure!

Yup 150psi

No I havent looked at thermal expansion not sure why that would be a problem now . The one thing I did not check was to see where my gas valve pressure was at. It is a new john wood tank with the thermal link that opens if the tank exceeds 200 F and the valve needs to be replaced if that happens



PT

If you have an expansion tank, it is probably shot. If you don't have one, you need one. A PRV produces a closed system, a waterlogged expansion tank means there's no place for the heated water to expand, increasing the pressure and dumping enough to relieve it out the T&P valve. Depending on your water quality, pressure, and maintenance, they can last anywhere from a few years to a decade or more, but will and do fail.