Your boiler has detected a minor internal setting inconsistency regarding when it should start heating, but it is unlikely to stop your hot water or heating from working.

What causes this fault?

This fault occurs when the boiler's control system identifies a mismatch in its internal operational settings, specifically regarding the temperature drop allowed before it fires up again. It is typically caused by a minor electronic glitch within the main control board or a slight calibration error in the temperature sensors. While the boiler continues to function, it is highlighting that its internal logic for managing heat cycles is slightly out of sync.