The furnace goes through the ignition cycle, when gas ignites it stays on for a couple of seconds and then quits. This repeats twice more then locks out. Yeah, I think its not sensing the fire either but where is the fire sensor on this model? I can't find it and there are only two wires going into the front chamber for the glow ignitor itself. This is a 1976 trailer that this furnace is in. PS. I've checked all the other limit switches that I can find and they're all passing voltage through.