My furnace keeps turning on and shutting off after about 10-15 seconds. I'm fairly certain the problem would be a dirty flame sensor, but I cannot for the life of me locate it on this model. Does this particular furnace not have a flame sensor? Or is it hidden in the belly of the unit? This is really bugging me, as most furnaces I've dealt with in my homes have had flame sensors that are fairly easy to locate. Any help is greatly appreciated.