I have a Trane XE80. Came home tonight and it was cycling thru the startup process, but no heat. I examined the error light it was flashing three times, then nothing then three times, etc. Indicating a pressure problem. Ipowered off the unit, tested the pressure switch, cleaned the tube and wiped the rollout sensors. powered it back on. I noticed the fast flash and electric ignitor lighting up but no gas flame. After a while the fan kicked on but no heat. Now when I turn the thermostat off the fan just runs and runs and the red light blinks twice over and over.

What's going on? How can I debug this?

It was the circuit board. I called the sop and they recommended tapping the on-board relays with the handle of a screwdriver. This caused them to close properly and the heater worked for that cycle. Had the board replaced after a cold weekend. Good times!

It broke on a Friday and was fixed the following Monday. It took me 5 months to get back here, I was running through me bookmarks and one brought me here. This site is a good resource but in my case there were no takers. Now, on to the dishwasher!