Lennox Furnace Error Code LED1 FAST FLASH / LED2 FAST FLASH

This pattern means normal operation is underway. Both LEDs flashing rapidly at the same time indicates the furnace control board has received a heating demand from the thermostat and is actively processing the startup sequence. No fault condition is present when this pattern is displayed.

Yes, it is completely safe. The dual fast flash pattern confirms the furnace is operating as designed and responding correctly to the thermostat. There is no safety concern associated with this specific LED status indication.

No repair costs are associated with this LED pattern because it indicates normal operation rather than a fault condition. If a technician is called and determines the furnace is operating correctly, you would only be responsible for the standard diagnostic or service call fee, which typically ranges from $75 to $150 depending on your region and service provider.

No corrective action is required for this LED pattern. It is a status indicator, not a fault code. If the furnace completes its startup and heats normally, no further steps are needed. However, if the LEDs shift to a different pattern or the furnace fails to produce heat after the startup sequence, further diagnosis of components like the igniter, gas valve, or flame sensor would be appropriate.

Resetting the furnace is not necessary and will not change anything meaningful in this situation. Because this is a normal operational status rather than a fault, the pattern will naturally transition as the furnace moves through its startup stages. Resetting would simply restart the sequence and the same pattern would reappear when the thermostat calls for heat again.