Your boiler is looking for an outdoor weather sensor that it can no longer communicate with, which might cause your heating to behave unpredictably.

DIY fix possible

Check if any external wires on the outside of your house leading to a small plastic box have been damaged or cut.Try resetting the boiler by pressing the 'R' or Reset button for five seconds.If you recently had building work near the boiler or outside walls, check if the sensor was accidentally unplugged.