Your boiler is simply reminding you that it is due for its regular annual service and there is no actual fault with the system.

Maintenance (only with weather-compensated control unit)

What causes this fault?

This code is triggered by the boiler’s internal timer, which tracks how many months or operating hours have passed since the last professional inspection. It is an automated reminder set by a heating engineer to ensure the system remains efficient and safe. There is no physical breakage or component failure causing this display; it is simply a proactive prompt for routine maintenance.