Lennox Air Conditioner Error Code E437

E437 is a heat sink temperature sensor fault on the inverter board of the outdoor unit. It means the sensor reported a temperature below 4°F or above 264°F after 10 minutes of operation, which triggered an inverter lockout coded internally as inverter code 65. The system shuts down to protect the power electronics from potential damage.

A full power cycle of the outdoor unit resets the inverter fault latch and may clear E437 if the cause was a transient condition such as a momentary airflow restriction or a brief electrical disturbance. If the underlying hardware fault remains, the code will return within 10 minutes of restarting operation. A reset is always the correct first step, but it is not a permanent fix if the sensor or inverter board has failed.

If the fault is cleared by a power cycle alone, the only cost is the service call fee, typically in the range of $75 to $150 depending on your region. If the inverter board requires replacement, parts and labor combined generally range from $600 to $1,500 or more, depending on the specific Lennox model, local labor rates, and part availability. Getting a quote from a licensed HVAC technician before authorizing parts is recommended.

The first step you can perform yourself is disconnecting power to the outdoor unit completely and then restarting it. If the fault clears and does not return, no further action may be needed. However, if the fault returns after the restart, replacing the inverter board is required, and that work should be performed by a qualified HVAC technician due to the high voltages present inside the inverter assembly.

No. The E437 fault causes the system to shut down as a protective measure, and you should not attempt to force continued operation while this code is active. Running an inverter with a faulty heat sink temperature sensor removes the thermal protection for the power transistors, which can lead to irreversible damage to the inverter board or, in a genuine overtemperature scenario, a fire risk.