Lennox Furnace Error Code DS1 Slow Flash / DS2 Slow Flash

On a Lennox furnace, DS1 and DS2 both producing a slow flash pattern indicates normal operation. The control board displays this status when the system is powered on and idle, when a cooling cycle is active, or when the thermostat is calling for continuous fan operation. It is a status indicator, not a fault code.

Yes, the slow flash pattern on DS1 and DS2 is a confirmation of safe, normal operation. The control board uses this pattern specifically to communicate that no fault conditions are present. The system is safe to operate in this state.

No repair is needed for this status indication, so there is no associated repair cost. If a technician visit confirms only the slow flash pattern with no underlying fault, the cost would be limited to the service call fee, which typically ranges from $75 to $150 depending on your location and provider. If diagnostics reveal a separate underlying issue, repair costs will vary based on the specific fault identified.

No corrective action is needed. The slow flash on DS1 and DS2 confirms the furnace is operating normally. If you expected the furnace to be heating but it is not, check your thermostat settings to confirm a heating call is active, then observe the control board for any change in the flash pattern that would indicate a fault.

Resetting the furnace is unnecessary because the slow flash is not a fault condition that needs to be cleared. After a power cycle, the control board will return to the slow flash pattern once it completes its startup self-check, confirming the board has re-initialized correctly. If you are seeing a different flash pattern that you believe indicates a fault, a reset may be appropriate for that specific condition.