Display shows A12; water heater indicates low pressure in heating circuit (for indirect systems).

Safety first: Allow the system to cool before opening bleed valves. Use only approved filling methods to avoid contamination.

This alarm indicates that the pressure in the primary (heating) circuit is below the minimum threshold.

• Step 1 – Check pressure gauge:
  • Locate the primary circuit pressure gauge; if below the recommended value (often ~1.0 bar cold), the system needs topping up.
• Step 2 – Top up system:
  • Connect the filling loop as per Nibe’s instructions.
  • Slowly open the valves and fill until the gauge reaches the target pressure.
  • Close the filling valves and remove the hose if applicable.
• Step 3 – Bleed air:
  • Bleed radiators and high points, then recheck pressure and top up again if needed.
• Step 4 – Reset alarm:
  • Reset A12 via the control panel.
  • Monitor pressure over several days; a drop indicates a leak that must be located and repaired.

If the pressure sensor reading is clearly wrong compared to a mechanical gauge, the sensor may need replacement.