I recently install a Kenmore #58240 40 gal. electric water heater. I had a 50 ga. approx. 12 yr. old Rheem which started to pop a little so I just decided to get a new one. After I installed it at factory set of 120° F, I noticed the TPR valve was cracking open and dripping as the water was being warmed up after usage.
I had the house pressure checked overnight using an outside faucet to record the house pressure for 24 hrs. and the meter showed that the 150 P.S.I. occurred thru out the night. My incoming water line meter was replaced around 6 yrs. ago and I was informed that the meter has a double check valve in it (closed system now).
My old water heater never had the TPR valve open even after they replaced the meter with the check valves in it. I do not have an expansion tank on the incoming line and am curious why I am seeing this pressure spike all of a sudden.
The service man came and replaced the TPR as a shot gun approach but I checked it immediately afterwards and the same dripping from the TPR valve occurred.