Your boiler has lost connection with its outdoor thermometer, meaning it might not adjust its heating efficiently based on the weather outside.

Outside temperature sensor is defective – check the connecting lead

What causes this fault?

This fault occurs when the boiler can no longer receive data from the sensor mounted on the outside of your home. The most common reasons are physical damage to the external unit from the elements or a break in the low-voltage wiring connecting the sensor to the boiler's main control board.