Your boiler has switched off because there is too much water pressure in the system, which can put unnecessary strain on the internal seals.

Water pressure too high - You have put too much water pressure in your system

What causes this fault?

This fault occurs when the water pressure inside your heating system exceeds safe operating limits. The most common reason is that the filling loop valve has been left slightly open or is leaking, allowing too much water to enter the system from the mains. Over time, this extra water pushes the pressure high enough that the boiler shuts down to protect its internal components.