Display shows A18; water heater indicates flow switch fault or no flow detected when pump is running.

Safety first: Turn off power and close isolation valves before removing any flow sensor or switch. Expect water spillage.

This alarm indicates that the unit does not detect sufficient flow when it expects it.

• Step 1 – Check valves and filters:
  • Ensure all relevant isolation valves are open.
  • Clean any strainers upstream of the flow sensor.
• Step 2 – Inspect flow switch:
  • Remove the flow switch or sensor body according to Nibe’s instructions.
  • Clean out debris and ensure the paddle or turbine moves freely.
• Step 3 – Electrical check:
  • Verify continuity of the flow switch when flow is present (technician task).
• Step 4 – Reset alarm:
  • Reassemble, open valves, bleed air, restore power, and clear the alarm.

Replace the flow switch/sensor if it fails mechanical or electrical tests.