Display shows A08; water heater indicates communication error with external heat source or accessory.

Safety first: Disconnect power to both the Nibe water heater and any connected external units before working on communication wiring.

This alarm indicates that the control board cannot communicate with a connected device (e.g. Nibe heat pump, accessory module).

• Step 1 – Verify wiring:
  • Locate the communication terminals (e.g. BUS, Modbus, or proprietary Nibe bus) on both units.
  • Check that the cable type and polarity match the installation manual.
  • Tighten any loose terminal screws.
• Step 2 – Inspect cable:
  • Follow the cable route and look for cuts, crushed sections, or water ingress at junction boxes.
• Step 3 – Power cycle:
  • Restore power to the external unit first, then to the water heater.
  • Allow several minutes for communication to re-establish.
• Step 4 – Check settings:
  • In the Nibe menu, verify that the correct accessory or heat pump type is selected.
  • Ensure addresses or IDs are set correctly if using a bus with multiple devices.

If communication cannot be restored, the communication module or main control board may require professional diagnosis.