Your boiler has detected that the water is getting hot too quickly or the temperature difference between pipes is too wide, often caused by poor water flow.

Maximum delta temperature (flow - return). Water circulation fault. Check central heating flow and return connection

What causes this fault?

This fault occurs when the boiler's internal sensors detect that heat isn't being carried away from the burner fast enough, causing the unit to overheat rapidly. The most common reason is a blockage in the system or a pump failure, which prevents water from circulating through the radiators as it should.