Your boiler is having trouble communicating with the outdoor weather sensor, which means it cannot automatically adjust its temperature based on outside conditions.

External probe fault

What causes this fault?

This fault occurs when the boiler's internal components detect a rapid, unsafe rise in temperature that cannot be dissipated. It is usually caused by a blockage in the pipework, a buildup of air, or a pump that has failed and stopped moving water through the system. In some cases, the temperature sensor itself may be faulty and providing an incorrect reading to the control board.