Trane VX95 Short Cycle Error Fixed by Cleaning Flame Rod

The suggested solution was to remove and clean the flame rod and reinstall it. After turning off the AC power at the circuit breaker panel and turning off the gas valve, I removed the flame sensor rod and sure enough, it had a slight coating of residue on it. A few seconds of scrubbing it with a piece of ScotchBrite pad gave it a nice shiny look. It was put back in place, power and gas turned back on, and the furnace fired and functioned normally again.

Trane VX95 Flame Sensor Rod Before and After Cleaning

Many thanks to grayfurnaceman!!! His

"Why does the gas furnace short cycle?" YouTube video, by grayfurnaceman

Hopefully, by posting this information other people will be able to remedy similar problems.

BTW, when I first went to turn off the local switch for the furnace, it did not work; the furnace kept running. Jiggling the lever made it work, but I replaced it out of an abundance of caution. This house was built in 1956, and the Slater 4200-SP appears to be the original. "Lifetime Switches" is molded into the bottom of the case, so I guess the 'lifetime' definition is up for interpretation (kind of like what the meaning of 'is' is). I was hoping it would be a mercury switch as was common with the early 'silent' type, since it initially did not make the familiar snapping sound when changing positions. It turns out the lack of a snap was a symptom of the switch not working at all. After exercising it a few times, the snap returned, but I will not bother re-installing it.

News Flash: I needed to do the same type flame sensor repair to my A.O. Smith GCV 40 100 gas hot water heater in June.

Posted December 16, 2015