:confused: What do you think is wrong with a relief valve that does not leak when the electric is turned off, but leaks when the electric is turned back on and mild(100 degrees or so) hot water comes from the faucets.:confused:

Replace it. When you shut off the power your water begins to slowly contract so there is a slight drop in pressure. When the power is on the water heats and expands, with all faucets closed, the pressure builds up a bit. Your PRV is right at the point of failing and should be replaced.

If you have a sprinkler system with a backflow preventer installed next to the meter you MUST have a expansion tank installed on the cold water inlet to the heater. Do you have such a set up without a expansion tank? If so all the new T&P valves in the world won't stop the leak. Regards, Tom

Tom is right. You may not even need a new PRV. It is just doing its job. Unfortunately, often once they open, they get crud on the seat and always leak then.