Hi
Our gas hot water tank made a bang noise last Saturday morning. Later in the day we noticed we had not hot water. My husband turned it off and was going to wait 5 minutes to relight. While waiting it made another bang. We turned off the gas and called a gas fitter person. He came the next day and vacummed (with a compressor) the whole thing out. Our hot water tank sits on a cement floor. He said we have to leave the door off suggested longer screws with washers so air is flowing in from the door. Our friend came later and put in one screw. Next day no hot water. My husband loosened the screw and it worked for a day. He took the screw right out and it worked for 3 days, the flame is blue and we don't want to call the gas fitter again, that already cost us $160. Anyone have any ideas? Does it need to be on legs?

This sounds like a newer sealed combustion water heater.

I've had no luck cleaning the bottom screen with compressed air or a vacuum.

You need to clean the bottom of the screen with a wire brush. As this area under the tank is very limited I had to fabricate my own round wire brush to accomplish this.

Good luck