Your boiler has sensed that the water inside is heating up far too quickly and has shut itself down to prevent damage.

Excessive temperature rise

What causes this fault?

This fault occurs because the water inside the boiler is getting too hot too quickly, often because something is blocking the flow or the pump has failed. The most common reasons include a buildup of internal debris like lime scale or sludge, or a mechanical failure that prevents the water from circulating around your radiators.