Your boiler is reminding you that its scheduled annual service is now due, but it should continue to provide heating and hot water as normal.

Control mode - Maintenance

What causes this fault?

This code is triggered by an internal countdown timer within the boiler's control unit, which tracks operating hours or calendar months since the last professional visit. It is not caused by a mechanical failure or a broken part, but rather a pre-set reminder to ensure the appliance remains efficient and safe. Once your Gas Safe engineer completes the maintenance work, they will reset this timer to clear the notification.