Your boiler has lost communication with the temperature sensor that monitors the outdoor solar panels or the system collector, meaning it cannot accurately manage heat levels for those components.

What causes this fault?

This fault occurs when the boiler can no longer receive data from the sensor attached to your solar heating panels. The most common reason is a physical break in the cabling or a failed electrical component within the sensor itself, often caused by long-term exposure to the elements or loose connections. Since the boiler cannot see how hot the solar panels are, it stops using them to heat your water as a safety precaution.