I think there are only two possible problems, the igniter itself is bad or the igniter board is bad. The metal tip of the igniter should be about 1/8" from the burner and you should be able to see and hear it when the gas starts flowing. Excessive space and the spark won't jump the gap or maybe a loose connection from the board to the igniter.
The board itself could be bad. There is a tester for the board and seeing as how it is under warranty, I'd take it to the dealer.
Testing is a 30 second thing with replacement of BO parts a little longer.
The procedure the heater will follow and trouble shooting instruction are probably in the manual.
Shutting down after a few seconds of no ignition is a built in safety feature, same as the FAU heater.
