[rtharwood]

I have a Trane XL80 heater about 14 years old. Heater worked fine last week. Now when you turn on the igniter does not activate and the red light flashes on initial start then remains on - does not flash. Could this be a defective igniter, flame sensor, thermocouple, controller, or something else completely? What would you recommend to change/ check first?

[gwr]

on those type of units it goes through a purge cycle , this is to purge any raw gas that might be in the combustion chamber. There is a fan switch (sail switch) that has to be made to let the control board know that the fan is running. If it does not engage then the unit will shutdown. There should be a listing on the unit that will tell you what the flashes stand for. I would check to make sure the combustion fan (purge fan) is operating then varify that the fan switch is made and that low voltage is going through the switch, no more than 24 volts. if this is working, then the next step is, the ignitor should start to glow if the flame sensor doesn't feel the heat from the ignitor the unit will shut down. Those are the only things at this point that will cause shutdown, Unless the control board is at fault. you can ohm out the ignitor and have a high reading, if it is burnt or broken you should be able to see this if you pull it out: Hope this helps.

[rtharwood]

Turned out to be the controller. Thanks for the input.