Lennox furnace error codes
9 codes from the Lennox furnace manual. Select a code for causes, safe checks and when to call a pro. View the source manual (PDF).
Improper main ground, OR line voltage below 90 volts. Control will not respond to a heat call until voltage rises above 95 volts.
Watchguard 1 hour: burners failed to ignite or lost flame 5 times during a single heating demand.
Circuit board failure or control wired incorrectly.
Main power polarity reversed. Switch line and neutral.
Pressure prove switch open, OR blocked inlet/exhaust vent, OR pressure switch closed before the combustion air inducer started.
Rollout switch open, OR 12-pin connector improperly attached.
Low flame signal: measures below 1.5 microamps. Replace flame sense rod.
Flame sensed without gas valve energized.
Primary or secondary limit switch open. Limit must close within 3 minutes or the unit goes into 1-hour Watchguard.