Display shows A20; water heater indicates maximum runtime exceeded for heater or pump.

Safety first: Turn off power before opening panels. Beware of hot surfaces and water.

This alarm indicates that the heater or pump has been running continuously beyond a safe or expected time limit.

• Step 1 – Check demand:
  • Ensure that hot water demand is not abnormally high (e.g. multiple baths in succession).
• Step 2 – Inspect for scale:
  • In hard water areas, limescale can severely reduce heat transfer. Check for scale on immersion heater and inlets.
• Step 3 – Verify circulation:
  • Confirm that the circulation pump is operating correctly and that all valves are open.
• Step 4 – Reset alarm:
  • After addressing issues, reset the alarm and monitor the time required to reach set temperature.

If the unit consistently hits maximum runtime, consider descaling or upgrading capacity with a Nibe technician’s advice.