Your boiler has detected that the water pressure has dropped too low or there is a problem with the internal sensor that monitors it, causing the system to shut down for safety.

Water Switch System pressure too low | Cause: Water Switch - plug disconnected, Waterswitch activated

What causes this fault?

This fault occurs when the boiler's internal safety mechanism detects that there isn't enough water pressure to operate safely. The most common reason is a physical leak in the system or air trapped in the radiators, but it can also be caused by a build-up of debris clogging the sensor or a loose electrical connection to the pressure switch.