We recently had a new hot water heater installed by a plumber. We keep the temp set medium hot. The water pressure into the house is under 90psi. Our problem is that the pressure release valve is dripping water. The plumber has replaced the valve and it does the same thing. He is suggesting an expansion tank to relieve this problem. My concern - is there a problem with the tank or is this fairly common. Our old tank leaked a little through the valve at first but stopped after a few weeks. This one is leaking much more now - more than a quart a day. There are 3 of us living in the house and it is a 50 gal tank. Thanks for any help you can give.