Your boiler is notifying you that your hot water circulation pump is currently active based on its programmed schedule, which may be an advisory rather than a breakdown.

What causes this fault?

This code is an status indicator rather than a mechanical failure, triggered when the boiler's internal clock activates the secondary hot water pump. It occurs because the system is following a pre-set schedule to ensure instant hot water is available at your taps. If you see this code when you don't need hot water, it usually means the timer settings in the control unit need to be adjusted to match your daily routine.