[Dano16]

Aire-Flo AF90MPE075 - on a call for heat the combustion blower runs, pressure switch closes, his glows and gas valve opens for a split second. Sometimes the inrush of gas is not enough to even ignite and sometimes it is enough to ignite across the burner but then goes out immediately. Again, this all occurs in less than 1 second - not enough time to eben attempt to prove flame.
After 5 or 6 trials the LED light flashes 3 times (pressure switch stuck open or closed). When a no call the switch is open, when combustion blower run it is closes - I even jumped it to make sure.
When 24V put directly to the gas valve it stays open until power taken away.
120V supplied to furnace. 25V from R to C. 120V from hot (black) to neutral (white) and ground.
My thoughts: bad ignition cntrl board. Am I missing something? TY

[Grady White]

Check your vent system. Make sure it is clear with no sags. Sags in a horizontal run will trap water & cause exactly the symptoms you have.