I have a trane ex 90 and during star up, or light off, it usually cycles or takes 2 tries before it lights. Natural gas by the way with electric pilot light. What is causing this? Been doing it for a season or two and usually lights on the second try. Thanks in advance
Monty

I think that model may have a hot surface ignition. Dirty burners or flame sensor will have that symptom along with bad gas valve or low gas pressure. If you can hear the gas passing through the burners when it tries to light I would check the ends of your burners for rust and clean them up.