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.