How is the water heater acting? I used to repair gas water heaters. Does the pilot light stay lit? Most of the time the gas valve is not the problem. Could be either the magnet in the valve, the thermocouple or just a dirty pilot.
The pilot would go out after a cycle and not relight. I could manually relight it. Rheem Tech Service said it needed a gas valve and the thermocouple was ok. (apparently)