Lennox Unit controller

Lennox Error Code 103

Unit controller

What It Means

  • ADVANCED CONTROL SETUP ERROR

Causes & actions from Lennox

How it shows
  • M4 alarm code: 103

Check CORE Unit Controller Configuration ID 1 settings.

Applicable models & manual sources
Disclaimer: This information is for general reference. Code wording and instructions vary by model. Always follow the service manual for your exact unit.

What should you check next?

Continue in ACLogics with guided diagnosis for your equipment and symptoms.

See how guided diagnosis works →