Electronic ignition, either glow coil or spark, comes on at temperature demand. Then the pilot will go out once the temperature has been satisfied. As stated above, with your model the common error seems to be either a flame sense problem or the vacuum switch prover protecting the exhaust venting. First check for blockage in the vent pipe. This could come in a form of a bird nest, water, or other blockage of some sort. Next check the clear vacuum tube on top of the heater. This is clear 1/4 inch tubing coming from the blower to the vacuum switch. As stated above push a paper clip thru the barb portion of the switch and blower where the hose attaches. Also make sure the hose is not loose at where it attaches. Also check any fan intake screen on the blower. Clean if needed.
Second would be a flame sense problem. This is much more difficult to check without the proper meters. A simpler but not always accurate method would be to check if your control valve is flashing a sequence code. If your model is of this kind then check the number of flashes against the error code sticker on your water heater and then report back your findings.