Lennox Furnace Error Code 8 Flashes

8 Flashes on a Lennox furnace indicates a lockout condition caused by the burners losing flame too many times during operation. The control board (103085) tracks each flame loss event and shuts the furnace down after repeated failures to maintain a stable flame. This is a safety feature designed to prevent unsafe ignition cycling. The furnace will remain locked out until power is manually cycled to reset it.

The furnace will not operate while locked out, so there is no active safety risk from the lockout state itself. However, you should not repeatedly reset the furnace without investigating the underlying cause. Repeated failed ignition attempts can indicate a gas supply or ignition problem that should be properly diagnosed before continued operation.

Repair costs depend on what is causing the repeated flame loss. Cleaning the flame sensor is a low-cost repair, typically in the range of $75 to $150 for a service call. Replacing a flame sensor or ignitor generally runs $100 to $250 in parts and labor. A gas valve replacement is more involved and can cost $300 to $600 or more depending on the part and local labor rates.

Start by turning the furnace off at the thermostat and cycling power at the breaker or power switch to clear the lockout. Then inspect the flame sensor rod for buildup and clean it if needed, check the gas supply to confirm the valve is fully open, and look for any blockages in the flue or venting. If the error returns after resetting, further diagnosis of the gas pressure, ignitor, and gas valve is required.

Yes, cycling power to the furnace at the breaker or the furnace power switch will clear the lockout and allow the control board (103085) to attempt ignition again. However, if the root cause is not corrected, such as a dirty flame sensor or low gas pressure, the furnace will lose flame again and return to the 8 Flashes lockout condition.