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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 8511
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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Lennox G26 Series, Propane Heating sequence starts, purge

Customer Question

Lennox G26 Series, Propane
Heating sequence starts, purge okay, coils glow, flame starts, then furnace for short while then shuts down before coming to heat and indoor blower starts. This process repeats three or four times then heat sequence stops. The symptoms are intermitent, ie the furnace heats normally sometimes other times the above occurs. Propane level is adequate.
Submitted: 1 year ago.
Category: HVAC
Expert:  Phil replied 1 year ago.
Hello, this combination of errors points to a bad printed circuit card. If it were just a dirty flame sensor rod, cleaning it off with plumbers sand cloth would have a good chance of restoring function.... but the blower comes on when it should not be coming on... that along with the flame sensing error points to a bad printed circuit card. Having said that, lets try cleaning the flame sensor rod and see if we get lucky or not. If that fails, do this heat stress test on the printed circuit card, that will reveal a bad card in about 50% of the cases. Use a hair drier to slowly warm the printed circuit card up to120For a bit warmer, but not over 140F... if there is any change in the error codes or other furnace behavior... the card has a cracked micro circuit that opens and closes as the card expands and contracts... that proves a bad printed circuit card.No change however does not prove the card is good however... but a change proves the card is definitely bad. The older a printed circuit card is, the more likely its bad, if the board has any dark or burned spots or corroded spots on it, its bad, often these are on the back side of the card, requiring removal to inspect for that. Stay in touch without any time limits until we get this resolved for you.