Hi this has been an occasional problem but now it is to the point that the furnace wont keep burning. When switched on it lights normally. They about 3 seconds later it cuts out. I'm sure its a sensor. How can we figure out which one is signaling a problem? Also what might the problem be? I mean could it be a bad sensor or does it mean something major? It has been running very strong. I think it may have to do with condensation.