To the OP, IF that water heater is more than 10 years old, I would REPLACE the gas valve. Atwood gas valves usually fail to "seal" after many years of service. What they do is, if you have the W/H OFF, spray soapy water all over the orifice and wait got 5 minutes, keep the orifice wet with soapy water. Odds are you will get bubbles indicating a leak. When I do a Manometer test on older RV's and it fails, this is the FIRST place I look. Most times it is leaking. This is NOT the cause of your problem, but I would do the test and replace if it fails. Doug
