Lennox furnace

[Dave]

It’s very possible the thermocouple or a dirty pilot orfice. I would buy a new thermocouple at the local harware store of furnace supply house and pull all the burners out and clean them. It’s not a real difficult job. turn off the gas and the electric, loosen the 5/16 screws that hold the manifold in place this will allow enough room to grab the burners and pull them out. if you lift them in the rear it will allow them to be removed. depending on the size of the furnace

82,000 btu = 3 burners 110,000 btu = 4 burners, 137,00 = btu 5 burner 165,000? = 6 burners. These are notorius for rust. Oh! you will need to remove the 1/4 inch pilot line and thermocouple in order to do this. But you should empty all the rust from the burners. Dis-assemble the pilot as there is a small pilot orfice in there that is probably full of dust. make sure you use a back up wrench. While the burners are out is a good time to inspect the heat exchanger! look up in the Duracurve heat exchanger and look for crack along the bends this is a common spot from expansion and contraction. re-installation is the reverse of removal. The burners have a knife edge that has to fit in the slot in the back of the heat exchanger to allow them to stay in place. also make sure that the carry over wings are lined up level. this is for the pilot to pass the flame over from one burner to the next. If they don’t line up well you may have a delayed ignition. install a new thermocouple. it should thread in to the valve hand tight and 1/4 turn more. don’t reef on it. The pilot flame should be blue. if it’s yellow its definately dirty. I’ve done this thousands of times. not real good at explaining by keyboard!! ha