Your boiler is reminding you that its annual service is now due to keep it running safely and efficiently.

What causes this fault?

This code is triggered by the boiler's internal timer reaching a pre-set limit of operating hours or months since its last professional inspection. It is not caused by a mechanical failure, but rather a deliberate reminder programmed by your engineer to ensure the appliance remains safe and valid under warranty. The code will remain visible until a qualified professional performs the service and resets the maintenance counter.