Lennox ML196UH070XP25B-05 about 8 years old with an intermittent ignition problem. Furnace will start and run properly 98% of the time. Unfortunately every once in a while (2 known times in 3 months) the furnace will not light the burners, the entire furnace continues to run for hours blowing cold air. The problem, so far, has corrected itself but living in Minnesota this is not an option. Furnace board stores last 5 error codes, pulled them today (only time ever) and it had recorded 4 errors in the following order. 6 pressure switch cycle lockout. 3 pressure switch open with inducer on. 2 Pressure switch closed with inducer off. 3 pressure switch open with inducer on. It seems to me if the burners do not light the furnace should shut down, not continue to run as normal but with no heat. I have an ecobee 3 thermostat which has bee working fine for the past 5 years, powering down the HVAC system does not fix anything, filters are OK, I checked the drains and they are clear. I would appreciate any insight anyone can provide. Thank you for your help.

  • Is there 24V from G to C when the blower is running? Also, is there a solid 24-28V from W to C during calls for heat? And can you post the wiring diagram for your furnace please? – ThreePhaseEel Mar 29 at 0:15

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