Lennox Furnace Error Code LED#1 ON / LED#2 Slow Flash

This code indicates that the rollout switch has opened, or that the 12-pin connector in the burner section is not properly attached. The rollout switch is a thermal safety device that trips when flames extend outside the normal combustion zone. The furnace shuts down to prevent a potentially hazardous condition until the cause is identified and corrected.

No, you should not attempt to run the furnace while this code is active without first determining why the rollout switch opened. Flame rollout is a serious safety hazard that can result in fire or carbon monoxide production. The furnace should remain off until a qualified technician has inspected the unit and confirmed the cause has been corrected.

Repair costs vary widely depending on the cause. Simple fixes like replacing an air filter or reseating a connector cost little to nothing beyond a service call fee, which typically ranges from $75 to $150. Replacing a rollout switch generally runs $100 to $250 in parts and labor. If a cracked heat exchanger is found, repair or replacement costs can range from $500 to over $2,000 depending on furnace age and part availability.

You can manually reset the rollout switch by pressing the button on top of the switch, but resetting it without finding the root cause is not a long-term fix. If the condition that caused the switch to trip is still present, it will trip again. A thorough inspection of airflow, venting, and the burner area should be completed before or immediately after the reset.

Resetting the switch will allow the furnace to attempt operation again, but the code will return if the underlying problem is not fixed. If the root cause is something like a dirty filter or a disconnected 12-pin connector, correcting that issue along with the reset should clear the fault. If the cause is a blocked flue, failed switch, or cracked heat exchanger, those repairs are required before the code stays cleared.