Your boiler is heating up too quickly and has shut down to prevent damage, usually because water isn't flowing through the system fast enough.

Flow temperature rise in heat exchanger too rapid

What causes this fault?

This fault occurs when the water inside the boiler heats up much faster than the system can carry it away, causing the internal safety sensors to shut the unit down. The most common reason is a blockage or a failing pump preventing the hot water from circulating through your radiators. It can also be triggered if your radiator valves are all closed or if there is excessive air trapped in the pipework.