Your boiler's outside temperature sensor is either giving an incorrect reading or has lost communication with the main control system.

Outside temperature with weather compensator – Vaillant controller only

What causes this fault?

This fault occurs when the boiler loses contact with the sensor located on the outside of your property, which is responsible for monitoring the outdoor temperature. The most common reasons are a break in the communication cable due to weather damage or a internal component failure within the sensor itself. Without this data, the boiler cannot automatically adjust its efficiency based on the weather conditions outside.