DAVE wrote at 2014-08-12 17:37:20
The pressure relief valve is more than likely releasing due to pressure and not temperature. Check the expansion tank. Too little air and the pressure goes up and down with the temperature. Too much air and the air can be introduced back into the system. does the tank have a bladder (schrader valve on top). If so, with pressure off the tank check the pressure with a tire gauge. It should be slightly higher than the setting you want. Depending on how high the water needs to be (one story, two story, three story)almost anything below 30 is ok but most likely 12-15 lb. If not add air. If when you check the pressure and water shoots out the bladder is bad and the tank needs replacing.