Display shows A13, often associated with very low or no system pressure indication.

Safety: Allow the system to cool before adding water. Do not overpressurize.

• Check pressure gauge: If pressure is below the recommended minimum, slowly open the filling loop and raise pressure to the specified level, then close the loop.
• Bleed air: After refilling, bleed radiators and recheck pressure.
• Inspect for leaks: Look around the Fondital heater and visible pipework for signs of water leakage. Repair leaks before refilling again.
• Pressure sensor tube: If fitted, remove and clean the small tube connecting the hydraulic block to the pressure switch or sensor.
• Replace pressure sensor: If pressure is correct but A13 persists, the pressure switch or transducer is likely faulty and should be replaced.