I have a 40 gallon direct vent gas water hetaer. New house built in 2002. I am currently on my third replacement water heater under warranty. The temp setting is low and gives plenty of hot water. The t&p valve keeps blowing and dripping when the unit runs. I thought maybe to much pressure so i installed an expansion tank on the hot water side that solved the problem for a month till the diaphram burst on the expansion tank and leaked. what else could be causing the tanks to go so fast. I have city water not well not sure of my pressure but comes out good at faucets any help would be greatly appreciated?