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

What causes this fault?

This code is triggered by the boiler's internal calendar once a pre-set timeframe has elapsed since its last professional inspection. It is not an mechanical failure, but rather a programmed reminder that the internal components need to be checked and cleaned to maintain efficiency. The code appears automatically to ensure the appliance continues to meet safety standards and remains within its warranty terms.