Lennox Furnace Error Code LED#1 Simultaneous Fast Flash / LED#2 Simultaneous Fast Flash

This LED pattern indicates normal operation. It is displayed by the integrated furnace control board the moment the thermostat sends a heating demand signal. Both LEDs flashing rapidly at the same time is confirmation that the call for heat has been received and the startup sequence is underway. No fault condition is present when this pattern appears at the beginning of a heating cycle.

Yes, this condition is completely safe. The simultaneous fast flash simply means the furnace has received a call for heat from the thermostat and is beginning normal operation. There is no safety lockout, no component failure, and no hazard associated with this specific LED pattern.

There is no repair cost associated with this LED pattern because it indicates normal operation, not a component failure. If a technician visit is needed to diagnose why a furnace is not heating despite showing this pattern, diagnostic service call fees typically range from around $75 to $150 depending on location and provider, with additional costs only if an actual fault is identified and parts are required.

No repair is needed. This simultaneous fast flash is a status indicator, not a fault or error code. If the furnace completes its startup and produces heat normally, the system is functioning correctly. Only if the furnace fails to produce heat after this indication should you look for a subsequent fault code that explains where the startup sequence stopped.

Resetting the furnace is not necessary and will not change anything in a meaningful way. This pattern appears during every normal heating cycle and will display again the next time the thermostat calls for heat. A reset is only warranted if a separate fault code appears after this indication and the furnace fails to heat.