Error code library

Lennox Heat Pump error codes

Search 1 diagnostic guide for Lennox Heat Pump faults. Each guide explains what the code means, what to check, and which part may be involved.

Diagnostic search

Find the exact guide you need

Search by brand, appliance, error code, symptom, likely cause, or replacement part.

1 guide found

Lennox communicator code E121 triggers when the outdoor unit low pressure switch detects unsafe refrigerant loss or freezing.