Your boiler has detected an issue with the sensor that monitors internal water pressure, meaning it cannot confirm if there is enough water to operate safely.

System pressure sensor

What causes this fault?

This fault occurs when the boiler's internal computer loses communication with the sensor that tracks water pressure. It is usually caused by a physical failure of the sensor's internal diaphragm or a loose electrical connection in the wiring harness. Because the boiler cannot verify if there is enough water to operate safely without damaging the heat exchanger, it will shut down as a precaution.