Thanks in advance for any guidance.
I have 2 Trane units, both running natural gas, and both about 6 years old. The larger of the two is in the basement and is running without issue. Its brother in the attic is an XB80, and is consitently losing flame right on the 2 minute mark.
Both units are running the same Hunter programmable thermostat.
Thinking it might be the thermostat sending a faulty signal, I swapped the Hunters and got the same results. Here are my steps:
1) Cut electrical power to furnace
2) Remove cover from XB80 unit
3) Turn gas feed on/off switch inside XB unit to "off"
4) Wait 5 minutes for any residual gas to disperse
5) Turn gas feed on/off switch inside XB unit to "on"
6) Restore electrical power to furnace
Within 15-20 seconds a reddish glow appears within the unit, and the gas ignites, presenting a full flow of blue flame. I am very encouraged at this point.
Almost exactly 2 minutes later, the flame abruptly disappears. repeated attempts produce the same result. There are various little clicks and pop sounds, but I cannot tell if this can be interpreted as the gas feed switch cutting the gas flow or not.
Again, suspecting the thermostat, I checked if the flameout was timed with the change of one minute to the next on the thermostat (i.e. thinking perhaps the thermostat sends new orders on the minute). No luck. Flameout is not timed with thermostat minute change.
Any help, hints or guidance would be greatly appreciated.
Thanks and best regards,