Your boiler is notifying you that a specific pre-set service interval or scheduled maintenance time has elapsed and a routine check-up is now required.

What causes this fault?

This notification is triggered by the boiler's internal timer reaching a pre-set date or number of burner operating hours. It serves as an automated reminder that the manufacturer's recommended maintenance window has arrived to ensure continued efficiency. It is not caused by a mechanical failure, but rather by the system tracking its own usage history.