What It Means
- Indoor temperature sensor (open/short error)
Lennox Air handler
Lennox Air handler Error Code 121
Air handler: Air handler (indoor)
Causes & actions from Lennox
How it shows
- Wired controller display: 121
This manual entry does not list further causes or actions.
Applicable models & manual sources
- MMD***M6-1P
Indoor temperature sensor (open/short error)
- MMD***S6-1P
Indoor temperature sensor (open/short error)
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.
