Lennox Furnace Error Code DS1 Fast Flash / DS2 Fast Flash

The DS1 Fast Flash and DS2 Fast Flash codes on a Lennox furnace indicate normal operation. They signal that the thermostat has initiated a heating demand and the control board has received that call. This is a status indicator, not a fault code, and no repair or reset is needed when the furnace is heating normally.

Yes, the DS1 and DS2 fast flash codes indicate normal, safe operation. There is no hazard associated with these status indicators. If you have concerns about combustion, unusual odors, or the furnace shutting off unexpectedly, those would be separate issues unrelated to this particular flash code.

There is no repair cost associated with this code because it indicates normal operation, not a malfunction. If your furnace is not heating properly despite showing this code, a diagnostic service call from a qualified technician typically costs anywhere from $75 to $150 or more depending on your region, and any parts required would be an additional expense based on what component is found to be faulty.

No action is required when DS1 or DS2 fast flash appears during a normal heating cycle. The code simply confirms the furnace is responding to a thermostat demand. However, if the furnace fails to complete its heating cycle after this code appears, you should watch for additional fault codes on the control board that would point to the actual problem.

Because DS1 and DS2 fast flash are status indicators rather than fault codes, there is nothing to clear. The flash pattern will appear each time the thermostat sends a heating demand and will stop once the heating cycle is complete or the thermostat is satisfied. Resetting the furnace is unnecessary and not recommended for this condition.