C2
Nibe
Accessory communication fault
C2 alarm, communication error with external accessory (e.g., Nibe SMO, ECS, or pool module)
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Safety Warning
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.
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Possible Causes
Disconnected accessory bus cable, incorrect bus wiring polarity, faulty accessory module, address conflict
How to Fix / Troubleshooting
Safety: Turn off power to all connected Nibe modules before changing bus wiring.
- Check bus cabling: Verify that the communication bus (e.g., Nibe BUS or Modbus) is correctly wired between the furnace and accessories. Observe polarity and shielding requirements.
- Reseat connectors: Unplug and firmly reconnect the bus connectors on each module.
- Check addressing: Ensure each accessory has a unique address set according to the Nibe installation manual.
- Restart system: Power up all modules and then the main unit. Clear the C2 alarm via the control panel.
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Repair Difficulty
Medium
3/5
Required Part
Communication Bus Cable
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