Atwood Water Heater ?

The ignitor fixed my problem. Thanks everyone

The heater can ignite the gas, and fail to detect that it is ignited, if there is a discontinuity within the igniter, or the lead to the igniter. Spark voltages can jump that gap, but the voltage used to sense the flame cannot, so no flame sensor current, board shuts down the gas shortly after the spark lights it.

Fix for that, in my case, was a new ignitor. Discontinuity was wire inside the insulator.

Chris, thanks for the response.

It runs a very small current through the spark gap and flame. Make sure the gap is in the flame, make sure the gap is 1/8 - 3/16", lightly sand the electrodes, tighten the burner mounting screws and lightly clean the connector on the circuit board with a pencil eraser.

More info at http://blog.rv.net/2008/02/lp-appliances-electronic-ignition-systems/