Your boiler has shut down because the water is heating up too quickly or hasn't been able to circulate correctly through the system.

Maximum delta temperature

What causes this fault?

This fault occurs when the internal sensors detect that water inside the boiler is getting too hot too quickly, or there is too large a temperature difference between the water leaving and returning to the unit. The most common reason is a lack of water flow, often caused by a failing pump or a blockage in the pipework that prevents heat from being carried away to your radiators. It can also be triggered if the sensors themselves become faulty and provide inaccurate temperature readings to the control board.