Lennox Furnace Error Code LED Flashing 2 sec on 2 sec off

This flash pattern indicates the burner control has entered Recycle mode. The furnace detected that the flame went out during an active heating cycle and is now holding in a 60-second delay before attempting to relight. It is not a full lockout, but it signals an intermittent combustion problem that should be diagnosed. If the condition repeats, the furnace may escalate to a lockout fault.

A power reset may allow the furnace to attempt another ignition cycle, and the flashing code may temporarily stop if the restart is successful. However, resetting does not fix the underlying cause of the flame loss. If the root issue is not corrected, the furnace will lose the flame again and return to Recycle mode or progress to a full lockout condition.

Repair costs vary widely depending on the root cause. Cleaning the flame sensor is often included in a diagnostic service call, which typically ranges from $75 to $150. Replacing a flame sensor part can add $20 to $80 in parts. A new gas valve or control board can bring total repair costs to $300 to $700 or more, and heat exchanger replacement is significantly more expensive, sometimes approaching the cost of a new furnace.

A homeowner can safely inspect and clean the flame sensor rod, check that the air filter is not heavily clogged, and ensure the gas shutoff valve is fully open. However, checking gas pressure, inspecting the heat exchanger for cracks, and replacing control components require specialized tools and should be handled by a licensed HVAC technician. Attempting gas valve or heat exchanger repairs without proper training carries serious safety risks.

The furnace may continue to attempt restarts on its own, but running it repeatedly with an unresolved flame loss condition is not recommended. If the cause is a cracked heat exchanger, continued operation could allow combustion gases to enter the living space, which is a carbon monoxide hazard. Have the furnace inspected by a qualified technician before relying on it for extended heating.