Your boiler is noting a change in how it reads the outside temperature, but it is typically just an internal setting update and should not stop your heating.

What causes this fault?

This code is triggered when the boiler's internal computer updates how it processes information from the outdoor weather sensor. It is essentially a background synchronization task where the system re-calibrates the temperature data to ensure your heating runs efficiently. It rarely indicates a physical breakdown and is usually just the software confirming its settings are correct.