I've had alot of trouble with those in the past.. Some of them had a recall on the heat exchanger, and the igniton modulor. ALso the recall had you turn the ignitor to it's side vs laying down flat. I don't recall the full model # of those recalls....
Also make sure the intake vent is letting air in (If there is one hooked up).
Also make sure the burners are lined up on the crossover bars.