Your boiler is confused about the weather outside because the external sensor has lost its connection, meaning the heating might not adjust correctly to the outdoor temperature.

Controls according to 0°C outside temperature - Outside temperature sensor lead break

What causes this fault?

This fault occurs when the electrical link between the boiler's control board and the sensor located on your outside wall is interrupted. The most common reasons are a loose connection at the terminal, a break in the thin communication wire, or internal corrosion within the sensor housing caused by moisture over time.