Trane XL80 flame sensor has been cleaned. The gas will light up and heat for 10 minutes sometimes longer but later the white rodgers controller unit led will change from flashing red light to constant red light. Then no more flame. Thermostat still is on and has not reached the chosen temperature setting.

When do you know for sure that the controller board is really bad and needs replacing when it seems to work after I unplug the furnace for a few hours?

If blower not working hit the reset then shut down heater for 2 hours then start back up this should sovle this problem