Lennox Furnace Error Code LED#1 Fast Flash / LED#2 Fast Flash (simultaneous)

This LED pattern indicates normal operation. Both LEDs flashing simultaneously at a fast rate means the furnace control board has detected a heating demand from the thermostat and the system is initiating its startup sequence. No fault condition is present, and no corrective action is needed.

Yes, this condition is completely safe. The simultaneous fast flash of both LEDs is a normal operational status, not a warning or fault. The furnace is simply signaling that it has received a heating demand and is beginning its startup process.

Because this LED pattern represents normal operation rather than a fault, there is typically no repair cost associated with it. If a technician is called to investigate and confirms the furnace is operating correctly, you may be charged a standard diagnostic or service call fee, which generally ranges from $75 to $150 depending on your region and the service provider.

No repair is necessary for this LED pattern. It is a status indicator confirming the furnace is responding correctly to a call for heat. If the furnace successfully heats your home during this display, everything is functioning as designed. Only investigate further if the furnace fails to produce heat after the LEDs have been flashing for several minutes.

Resetting the furnace is not necessary and will not permanently change this display, because the pattern is tied to an active thermostat demand rather than a stored fault. As long as the thermostat is calling for heat, the LED pattern will reappear after any reset. The pattern will change on its own once the heating cycle progresses or the thermostat demand is satisfied.