I have a Trane XE 70 furnace. Here is my situation. The furnace has electronic ignition which appears to be working fine. The burner will only light sporadically. I can get the burner to light if shut-off power to the furnace and turn it back on.
I did notice that when the burner was working, the fan would turn off prior to hitting my temperature set-point. It would do this several times before reaching set-point. I expected the furnace to overheat and shut-off the burners, but this did not happen.
In any event, I had a techincian come out and the were not able to daignose the problem. They fell back on the statement that the furnace was 18 years old and should be replaced.
I have changed the thermostat and will monitor that to see if it corrected the problem. Any thoughts on this * Is additional info needed to assess this *