My hot water heater was replaced last August, 2004. I was away for a month over the summer and I turned it down to vacation temp. A little while after I returned, the hot water started to smell bad. It happens at every faucet including the shower, and only when I have the hot water running. I have had a plumber in for other reasons and asked him about it - said it didn't smell like rotten eggs and the brand hot water heater doesn't usually have a problem with heating elements. He put bleach into the tank, which seemed to do away with the smell for a little while. Now, about a month later, the bad smell has returned. Does this mean I have bacteria in my tank? If I turn the water heater up hotter for a while, might it kill the bacteria?

speedball1

Sure sounds like bacteria to me. Chances are he didn't load the tank up with enough bleach or you may try hydrogen peroxide in quantity . Failing that you might want to check out a commercial germicide at; http://www.biocide.com/gramicid.html
Good luck, Tom