Your boiler's internal sensor that monitors water pressure has experienced an electrical failure and can no longer tell if there is enough surface water for the system to run safely.

What causes this fault?

This fault occurs when the boiler's internal computer loses communication with the water pressure sensor, often due to an electrical short or a component failure inside the sensor itself. Without a reliable reading, the boiler cannot confirm there is enough water to operate safely and will shut down to prevent internal damage. The most common reason is general wear and tear of the sensor's electronics, though a loose connection in the wiring can also trigger the error.