Your boiler has likely overheated because the water isn't moving through the system properly or a safety sensor has detected a temperature that is too high.

High limit protection – possible flow temperature sensor not active or incorrectly located, no system circulation

What causes this fault?

This fault occurs when the water inside the boiler exceeds a safe temperature, triggering a safety shutdown. The most common reasons are a pump failure that prevents water from moving, or a buildup of debris and sludge that blocks the heat exchanger.