What It Means
- FWM SOFTWARE MISMATCH
Lennox Unit controller
Lennox Error Code 520
Unit controller
Causes & actions from Lennox
How it shows
- M4 alarm code: 520
Firmware Update Failed: Software Mismatch between M4 and W4
Applicable models & manual sources
- MODEL L - M4 UNIT CONTROLLER
FWM SOFTWARE MISMATCH
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.
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