: I have a timer on my water heater. After being on for 15-30 minutes, : hot water begins flowing copiously out of the relief valve at the top : of the heater. The relief valve seems to be working. Is this a thermostat : problem. Do I need to replace both thermostats? If I only need to replace : one, how do I tell which one to replace? water expands as it heats,you may have a check valve at the heater causing excessive pressure as it reheats. an expansion tank may be needed. does the water quit flowing when the elements have reached it setting. if the water is excessively hot then the thermos are probably bad. both should be changed. it is hard to tell which one is really bad. hope this helps.
