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

When DS1 and DS2 both flash slowly at the same time on a Lennox furnace control board, it indicates normal operation. The system is either powered on in standby, actively running a cooling cycle, or operating in continuous fan mode. This is a status indicator, not a fault or error condition.

Yes, this condition is completely safe to operate under. The simultaneous slow flash on both LEDs is the furnace's way of confirming normal, healthy operation. There is no risk associated with this indicator pattern.

Because this indicator reflects normal operation rather than a fault, there is typically no cost associated with it. If a technician visit is needed to confirm system operation or investigate a comfort complaint alongside this status code, diagnostic service call fees generally range from $75 to $150 depending on your location and provider.

No repair or reset is needed when both LEDs flash slowly together. This pattern confirms the control board is functioning correctly. If the system is not delivering heating or cooling despite this normal status signal, the issue lies elsewhere, such as at the thermostat, blower motor, or refrigerant system.

Resetting the furnace is not necessary and will not change this pattern in a meaningful way. After any power cycle or reset, the control board will return to this same slow dual flash once it completes its startup sequence, because this is the normal operating state. Resetting should only be considered if a separate fault code has appeared.