Your boiler has lost its connection to the weather sensor that sits on the outside wall of your home, meaning it doesn't know how cold it is outside to adjust your heating automatically.

DIY fix possible

Locate the external sensor box on the outside of your propertyCheck that the wiring at the sensor box has not been damaged or knocked looseInspect the terminal connections to ensure there is no corrosion or water ingressIf the wiring is broken, it will likely need to be replaced by a professional