I have major water pressure creep all the time. New water heater installed with expansion tank and the pressure is being relieved by the pressure release valve. I have tested the lines with a pressure gauge and the flow is regulated at 40-50 psi when running. The gauge registers a high of 150 psi over night which triggers the release valve. I have tested the line with the water heater turned off so I know it's not thermal expansion. My question, is the pressure regulator valve on the incoming line supposed to shut off the inlet when the line pressure reaches the set psi at say 50 or do they usually allow the pressure to continue? Do I need a different valve to keep out the higher pressure? I am the last house at the end of the street and I believe the water main ends here and does not continue. Not sure if the pressure regulator valve is bad as it does regulate when running. Thanks for the help.