Display shows A10; water heater indicates electric heater fault and may disable immersion heating.

Safety first: Isolate power at the main breaker and verify with a tester before touching heater terminals. Risk of electric shock.

This alarm indicates that the electric immersion heater is not functioning correctly.

• Step 1 – Visual inspection:
  • Remove the heater access cover on the Nibe cylinder.
  • Check for signs of overheating, melted insulation, or burnt smell around the heater terminals.
• Step 2 – Check connections:
  • Tighten any loose terminal screws on the heater and contactor.
  • Inspect the wiring harness for discoloration or damage.
• Step 3 – Continuity test (qualified persons only):
  • With power off, disconnect the heater leads.
  • Measure resistance across the heater; an open circuit indicates a failed element.
• Step 4 – Reset and test:
  • Restore power and clear the alarm.
  • Monitor current draw (if you have a clamp meter) and verify that the tank temperature rises when the heater is enabled.

Replacement of the immersion heater or contactor should be performed by a qualified electrician or Nibe service technician.