Lennox Heat Pump Error Code 8

Error code 8 on a Lennox heat pump indicates a welded contactor condition, where the compressor is running continuously because the contactor has failed to open. This can be caused by a physically stuck contactor or by the thermostat demand signal not being properly connected to the control module. The system flags this because the compressor is operating when no demand signal is present, which points to a failure in the switching circuit.

A welded contactor means the compressor may be running without any demand, which puts unnecessary wear on the compressor and can lead to system damage over time. Continuous compressor operation without proper cycling can also cause refrigerant and pressure issues. It is recommended to shut down the system and have it inspected promptly rather than continuing to operate it with this fault active.

Resetting the system may temporarily clear the fault code, but if the contactor is physically welded shut or the thermostat demand signal wiring is incorrect, the underlying problem will remain and the code will return. A reset does not fix the mechanical or wiring issue causing the fault. The contactor and wiring must be inspected and corrected before the system will operate normally.

Diagnosing and replacing a contactor involves working inside the unit near high-voltage components, which carries serious safety risks. Knowledgeable DIYers comfortable with electrical safety procedures can inspect the contactor and check wiring connections, but replacing the contactor or diagnosing control module faults is generally best handled by a licensed HVAC technician. At minimum, disconnect power to the unit before opening the access panel.

If the fix is simply a wiring correction at the thermostat demand signal terminal, the repair cost may be limited to a service call fee, typically in the range of $75 to $200 depending on your area. If the contactor itself needs replacement, parts and labor combined generally fall in the range of $150 to $400. Control module replacement, if required, can push costs higher, often $400 to $800 or more.