hot water heater problem

[tom41]

I have a suburban 6 gallon WH, that is electric/gas., I have always used it on electric for serveral yrs., never on gas. The other day I cut the electric off and turn the switch for the gas (gas is on) it started up, burned with a blue flame for mabe 30 seconds , shut off, did this 3 times but would not keep on. The electric was off long enough that the water was cold. Works perfect on electric. Any suggestions what to check next?
thanks
Tom

[Gary RVRoamer]

I'm not an expert on Suburban heaters, but that sort of symptom usually means the controller bard is shutting down the gas becasue it has not sensed a flame in the burner. That's a safety feature. The heater should have a sensor at the point where the flame burns in the tube so it can detect the heat of a flame. If that sensor fails, or the wiring gets corroded, the controller board won't detect the flame and will shut things down in 15-30 seconds.