Your boiler is currently preparing or delivering hot water, which is a normal operating status of the pre-heat function rather than a failure.

Check diagnostic code. (turboMAX Plus only) check diverter valve spindle against blade lightly. Replace diverter valve.

What causes this fault?

This status occurs when the boiler's internal pre-heat function, known as Warmstart, is active to ensure hot water is available quickly. It is triggered either by the boiler periodically heating its own internal store or when you turn on a hot water tap. This is part of the appliance's normal operation and indicates the system is working as intended to maintain comfort.