Lennox Furnace Error Code DS1 Fast Flash / DS2 Fast Flash (simultaneous)

This simultaneous fast flash on both DS1 and DS2 LEDs is a normal status indication, not a fault. It signals that the thermostat has initiated a heating demand and the control board has received the call for heat. The furnace should proceed through its normal startup and heating sequence. No service or repair action is required for this indication alone.

Yes, this condition is completely safe. The simultaneous fast flash is a normal operational indicator, not a warning or fault condition. The furnace is designed to display this pattern at the start of every heating cycle. You can operate the furnace normally.

Resetting the furnace is not necessary for this pattern, as it is not a fault code that needs to be cleared. The flash pattern will naturally stop or change as the furnace progresses through its heating cycle. If you cycle power to the furnace and the pattern reappears when the thermostat calls for heat, that is expected and normal behavior.

No repair is needed when this pattern appears. The simultaneous fast flash on DS1 and DS2 confirms the furnace is responding correctly to a thermostat heat call. If the furnace completes its heating cycle normally, everything is working as designed. Only investigate further if the furnace fails to complete its heating sequence and a different fault code appears.

There is no repair cost associated with this flash pattern because it indicates normal operation, not a fault. If you are seeing this code and the furnace is otherwise running correctly, no parts or labor are needed. If the furnace is also failing to heat properly, a technician would need to diagnose the underlying issue, with service call costs typically ranging from $75 to $150 or more depending on your area.