I have a forced hot air Trane xe 80 furnace. Electronic ignition. At times the burner will not ignite. The fan motor runs and only cold air is coming out. If I turn the furnace switch off then on again, it will glow and then the burner will ignite. This could last for days, then it will do it again.

Here a few things to check. Trane has a screen in the air intake port of this furnace. It blocks any debris from entering the combustion chamber. I have found that if a leaf got to the screen and as the temperature dropped, Ice started forming and increasing the size of the restriction to the point where the furnace just stopped. Really! If you experience the no-heat condition on days when there is ice in the air or the temperature dropped suddenly, you may have this condition. Take a very powerful flashlight, one that you can focus the beam and look up through the viewing window at the top of the burner box. By looking at the bottom of the center pipe, you will see lots of small round holes. This is the screen. Focus the beam to see if you can detect any debris caught on the top side of that scree. If so you will need to remove the center PVC pipe from the top of the furnace and clean out the debris. Because this pipe is the fresh air coming into the furnace, It is fine to not glue it back into place but seal the outer edge only with some silicone. You will find that you may need to cut the old pipe about 2" above the furnace to be able to access it. If so, just get a new coupling and pop it in.

If it continues, you may be looking at either a build up of water in your venting system or a weak circuit board. Make sure the venting system pitches back toward the furnace so any accumulation of water gets drained out through the condensate drain. Clear away any obstructions from both the air intake and exhaust pipe outside and check to see if you are not sucking the exhaust air back in as the furnace runs.

Try cleaning your flame sensor with sandpaper.

I have/had the same problem with my xe90. Changed PC boards only to get another but similar problem. I eventually discovered that there was NO ground on the unit and after running a wire to the water pipe the problem seems to be fixed, hopefully. The PC boards are extremely sensitive to polarity and the ground and can actually eat themselves up over time if not grounded. This is something I would check... Good luck.