Furnace/heat pump stops and displays A1 alarm, no heating or hot water

Safety first: Turn off power to the Nibe furnace/heat pump at the main switch and allow the unit to cool before opening any panels. Do not bypass any safety switches.

Step‑by‑step:

• Check system pressure and circulation: Verify that all radiator/underfloor heating valves are open. Ensure the circulation pump in the Nibe unit is running (you should feel vibration when powered). If you have external circulation pumps, check they are powered and not seized.
• Bleed air from the system: Use the bleed valves on radiators and high points in the system to remove trapped air. Top up system water via the filling loop to the pressure recommended in the Nibe manual (typically around 1–1.5 bar when cold).
• Inspect filters and strainers: Clean any Y‑strainers or Nibe inline filters on the heating circuit. A clogged filter can cause high pressure on the refrigerant side.
• Reset the alarm: Restore power, then use the Nibe control panel to reset the A1 alarm (menu path varies by model, typically via Alarm → Reset). Observe operation; if the alarm returns quickly, stop the unit.
• Check the high‑pressure switch wiring: With power off, inspect the high‑pressure switch on the refrigerant line for loose connectors or damaged wiring.

When to call a technician: If the A1 alarm recurs after basic flow checks and bleeding, a certified Nibe technician must check refrigerant charge, high‑pressure switch function, and system design. Do not attempt to open the refrigerant circuit yourself.