Lennox Furnace Error Code LED1-ON/LED2-SLOW_FLASH

This LED pattern signals that the rollout switch has opened, cutting power to the burner system as a safety precaution, or that the 9-pin control board connector is not properly attached. The rollout switch is a thermal safety device that responds when heat or flames escape the combustion chamber. The furnace will not operate until the switch is manually reset and the underlying cause is identified and corrected.

No, you should not continue operating the furnace after this error without a proper inspection. A rollout condition means heat or flames have moved outside the combustion chamber, which poses a fire risk and may indicate a cracked heat exchanger or serious venting problem. The furnace should remain off until a qualified technician determines the cause.

Repair costs vary widely depending on the root cause. If the issue is simply a loose 9-pin connector or a minor venting blockage, costs may be limited to a service call fee, typically in the range of $75 to $150. If the heat exchanger is cracked, replacement can range from $500 to $1,500 or more depending on the unit. Inducer motor replacement generally falls in the $300 to $700 range including parts and labor.

Locate the rollout switch near the burner assembly and press the small button on the top of the switch to manually reset it. The furnace will not restart until this reset is performed. However, resetting the switch without finding and fixing the root cause of the rollout condition is not safe, as the switch will trip again or a more serious hazard could develop.

Pressing the reset button allows the furnace to attempt operation again, but it does not fix the underlying problem. If the condition that caused the rollout is still present, the switch will open again and the LED1-ON/LED2-SLOW_FLASH code will return. Permanent resolution requires diagnosing and correcting the root cause, such as clearing a blocked flue, repairing the heat exchanger, or replacing a failing inducer motor.