Lennox Furnace Error Code LED-OFF

LED-OFF on a Lennox furnace with the G776 ignition control (-1 and -2 models) means the diagnostic LED on the control board is completely dark. This indicates a control failure, a loss of power to the furnace, or a hard lockout condition. A fully dark LED is abnormal and signals that the board is not operating. The condition requires active diagnosis to determine whether the board itself has failed or whether an external issue like a power or gas supply problem is responsible.

No, a furnace showing the LED-OFF condition will not operate normally and should not be forced to run. The G776 control manages ignition and safety functions, so a failed or locked-out control board means the furnace cannot safely regulate the heating cycle. Leave the furnace off until the cause of the LED-OFF condition is diagnosed and resolved.

A thermostat reset will clear the condition permanently only if the underlying cause was a temporary hard lockout or a brief interruption in power or gas supply. If the G776 ignition control board has suffered an internal failure, the LED will remain off after the reset and the condition will not clear without replacing the board. If the LED comes back on after the reset but the furnace continues to fault repeatedly, further diagnosis of the ignition system is needed.

Yes, you can attempt a reset by removing the thermostat demand for at least 30 seconds, which means lowering your thermostat setpoint below room temperature so the furnace stops calling for heat. After 30 seconds, restore the heat demand and observe whether the LED comes back on. If the LED remains off after this reset attempt and power and gas supply are confirmed to be working, the G776 ignition control board has failed and will need to be replaced.

If the issue is simply a tripped breaker or a hard lockout that clears with a reset, there may be no parts cost at all. If the G776 ignition control board has failed and needs replacement, parts and labor costs typically range from $200 to $600 or more depending on your location and the specific board required. Getting a quote from a licensed HVAC technician before authorizing the repair is always recommended.