Replaced the keypad 2 years ago, unit is 10 years old, I've checked the flow pressure sensor, checked the air blower sensor, and don't know whether the thermister and exhaust is normally opened or closed. It's open now and don't know if that's preventing start up. Appears as though all the safety's are operational.
Any help would be appreciated.

Pool & Spa - Sta Rite - Sr333na Max E Therm Pool & Spa Heater Dual Electronic...