Your boiler has sensed that parts of the internal system have become too hot, causing it to shut down automatically to prevent damage.

Overtemperature protection intervention

What causes this fault?

This fault occurs when the internal temperature of the boiler rises above a safe limit, usually because water isn't moving through the system fast enough to carry heat away. The most common reasons are a failing circulation pump, a build-up of sludge or limescale blocking the heat exchanger, or a 'pocket' of air trapped within the unit.