Lennox Heat Pump Error Code Alternating SLOW Flash

The alternating slow flash on a Lennox heat pump indicates the system is in a 5-minute anti-short cycle delay. This delay activates at initial power-up, after a room thermostat demand ends, or following a safety trip event. It is a protective function designed to let refrigerant pressures equalize before the compressor restarts. In most cases, the system will resume normal operation automatically once the 5 minutes have elapsed.

Yes, the alternating slow flash is not a warning of a dangerous condition. It simply means the unit is in a timed hold before the compressor restarts. The system is functioning as designed during this state. However, if the delay is triggered frequently by a recurring safety trip, the underlying cause of that trip should be diagnosed to avoid long-term compressor damage.

If the delay is part of normal operation, there is no repair cost at all. If a safety device trip is the cause, diagnostic and repair costs will depend on the specific component involved, such as a pressure switch or refrigerant recharge, and can range from $100 to $600 or more. If a control board replacement is needed due to a timing circuit fault, parts and labor costs typically range from $300 to $700 depending on the model and local labor rates.

In most situations, no repair is needed because this is a normal protective delay. Simply wait 5 minutes and the system should restart on its own. If you are a technician needing to speed up diagnostics, you can jumper the TEST pins on the control board to override the delay. If the delay keeps repeating, investigate whether a safety device such as a pressure switch or thermal overload is tripping repeatedly.

Cycling power to the unit will not skip the delay, as the control board will simply restart the 5-minute anti-short cycle timer from the beginning upon power restoration. The only way to bypass the delay intentionally is to jumper the TEST pins on the control board. Waiting out the 5-minute timer is the standard resolution for normal operation.