I am working on a trane XE80 with an intermittant lighting problem. This is what I am seeing.
1. When I first turn on the thermostat after it's been off for a while everything lights off fine and the furnace will run for a while (like 1 - 1.5 hours) before it turns off before hitting the thermostat temperature.
2. Furnace waits a couple minutes before it restarts the ignition sequence.
3. Ignition sequence starts, gas valve opens (can hear the hiss), but the hot surface ignitor is clearly not glowing this time around and there is no ignition. Repeats two more times then locks out.
4. Turning the thermostat off and on to reset the lockout SOMETIMES fixes the problem temporarily.
Any thoughts to the problem?