I have Trane XV90 that was blowing cold air while it was on heat. I have recently changed the ignitor (which seems to work just fine) and the flame sensor (which seems to be failing already). I just caught the furnace in a cycle of trying to turn on but going out repeatedly. So I turned off the power and turned it back on, and the ignition cycle was successful on the first try. Could this mean that there is something wrong with the board? This is my 3rd flame sensor in a couple of months so I think that the flame sensor itself should be fine. I would really appreciate any thoughts.


  • Are you getting codes from the board? – ThreePhaseEel Jan 4 '18 at 3:03
  • Sounds like a plenum over heat sensor; either broken or doing it's job. – Mazura Jan 4 '18 at 6:39
  • You haven’t really given enough information but I can tell you that it is most certainly not the flame sensor. In all my years servicing furnaces I have never seen a bad flame sensor let alone 3. It is only a wire and a rod with ceramic to prevent it from grounding. They occasionally get dirty though. If it goes out within 5 seconds of lighting it is most likely the circuit board or a grounding problem. You can easily test the sensor. It should be about 0 ohms resistance. Most circuit boards run about 4 milliamperes, run a meter in series with the sensor. – user76730 Jan 6 '18 at 5:47

It might be the flame rollout switch, try resting it and see if it works.

The flame rollout switch (typically mounted on the side of the burner box) is a safety device which senses a hot flame or exhaust and shuts down the furnace to prevent a fire or carbon monoxide buildup in your house. Once it has tripped the furnace will not start unless you reset it

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  • Thanks so much for your reply. What is the rollout switch please? – John Jan 4 '18 at 0:00

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