Help - intermittent combustion heater

[MikeZ]

HELP please. My 79 P337-H combustion heater has become intermittent. Last trip from Florida to Upstate NY was almost hellish (cold). Heater fires, gets warm, works on the ground, goes out after 5-10 minutes in flight. Will re-fire, but not stay on, sometimes seems to not want to fire.

The heater was JUST replaced with an O/H unit. The old one had identical symptoms. We also just replaced the floor mounted thermostat. All accessories with the heater are new including a new fuel pump.

We are just checking and servicing the combustion air blower, which has not been serviced yet. This may or may not work (we'll find out).

Short of pulling and replacing every single wire in the system, can anyone suggest a magic bullet?