Hi, My wife and I just purchased our 1st home. It has been vacent since March of this year, so it has some cobwebs so to speak. We have two gas water heaters, and when I turned them on yesterday they fired right up. A little while later one of the water heaters starting hissing pretty good. I had it set on the 'C' level on a four step scale with 'D' being the highest. So, I lowered it all the way down till the hissing stopped. Then I raised it to A, and no hissing, then B, hissing...so I lowered it back to A. IT takes a little while or the water to get hot from the faucet in the kitchen, but once its there its hot. Could this hissing be due to it sitting for so long? Should i do a flush and see what happens? I did a visual insection and saw no pressure relief valve discharge. Is this a case of it sitting and needing some action?