quote:Originally posted by LazyPup
There is one possibility that should be checked. Look under the gas control and you will see a service access cover into the combustion chamber. On the new water heaters the service access is sealed, but on older models there is supposed to be a galvanized metal cover that fits rather loosely inside the access. If that cover is missing, under rare circumstances a draft of air near the floor can push the raw gas back away from the pilot flame as the burner comes on. In that situation the combustion chamber fills with a bit more gas before the gas reaches the Pilot flame and causes ignition. The end result is when the gas ignites it tends to flash back and would cause some of the gas or combustion by products to vent out through the service access. Normally if the draft cover is missing or mis-positioned there will be faint traces of black soot on the outside of the water heater immediately above the access opening.