Lennox Heat Pump Error Code 9

Error Code 9 means that a safety device wired into the Option 1 input circuit on the control board opened its switch after the compressor had been running for more than five minutes. This is a protective fault that shuts the system down to prevent equipment damage. The control board monitors this circuit continuously during compressor operation, and any interruption after the five-minute mark triggers the lockout.

Resetting the control board may clear the fault temporarily, but if the underlying cause of the Option 1 safety device trip has not been corrected, the error will return once the compressor runs for more than five minutes again. A reset should only be performed after inspecting the safety device and its wiring to understand why the circuit opened.

Repair costs depend entirely on what caused the safety device to trip. Simple wiring repairs or cleaning a dirty condenser coil may cost relatively little, typically in the range of $75 to $200 for a service call. If the fault is caused by a refrigerant charge issue or a failed component such as a pressure switch, costs can range from $150 to $600 or more depending on parts and labor in your area.

Start by checking the safety device wired into the Option 1 circuit and all associated wiring for loose connections, corrosion, or visible damage. Identify whether the device is a high-pressure switch, low-pressure switch, or another field-installed component, and evaluate whether that device tripped for a legitimate reason such as a refrigerant pressure problem. Resolving the underlying cause of the trip, rather than simply resetting the fault, is the correct fix. A licensed HVAC technician should handle refrigerant-related diagnostics.

No. Error Code 9 indicates a safety device is actively detecting an out-of-range condition in the system. Continuing to operate the unit without diagnosing and correcting the fault could result in compressor damage or other component failures. The system should remain off until a technician has identified and resolved the cause of the trip.