Your boiler is simply reminding you that its annual service is now due, and it does not indicate a breakdown or a safety fault.

Reset service reminder

What causes this fault?

This code appears because a pre-set timer, calibrated by your heating engineer during their last visit, has reached its annual limit. It is not triggered by a mechanical failure, but rather by the boiler’s internal clock reaching the 12-month interval for professional maintenance. Once this threshold is met, the display alternates between the temperature and this code to prompt you to book a safety check.