Boiler displays U9; control functions limited or locked

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

Possible Causes

Incorrect service parameter settings, Incompatible control module installed, Corrupted control board memory

Safety: Only trained personnel should change service parameters.

1. Note current settings: Before making changes, record all current parameters from the Buderus service menu.
2. Restore defaults: Use the service menu to restore factory default settings where appropriate.
3. Check module compatibility: Ensure any added modules (e.g., mixing module, solar module) are compatible with the boiler model and firmware.
4. Firmware update: A Buderus technician may update the control firmware if corruption is suspected.

Hard 4/5

Control Board / Configuration

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