Your boiler has shut itself down because it has detected that it is getting far too hot, usually due to a lack of water flow or a circulation blockage.

Safety switch-off: Temperature limiter - Maximum temperature at the flow/return temperature sensor is too high when the safety cut-out function is operating using the NTC

What causes this fault?

This fault occurs when the boiler's internal water temperature rises too quickly or exceeds a safe limit, triggering an emergency shutdown to prevent damage. The most common reasons are a seized pump failing to move water, a buildup of sludge blocking the heat exchanger, or air trapped within the system preventing proper circulation.