What It Means
- PHASE MONITOR FAULT
Lennox Unit controller
Lennox Unit controller Error Code 20
Unit controller
Causes & actions from Lennox
How it shows
- M4 alarm code: 20
External phase monitor is indicating an issue.
Applicable models & manual sources
- MODEL L - M4 UNIT CONTROLLER
PHASE MONITOR FAULT
MODEL L - M4 UNIT CONTROLLER, M4 Unit Controller
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.
