Your boiler is reporting an issue with the solar panel temperature sensor, which usually means the system is detecting an unusual reading from your solar thermal panels.

Collector temperature: Is only displayed, if a solar module is connected.

What causes this fault?

This fault occurs when the boiler's control system loses communication with the sensor that monitors the temperature of your solar panels. The most common reason is a broken or corroded wire between the roof and the boiler, or a sensor that has failed due to extreme weather exposure. Because the boiler cannot tell how hot the panels are, it stops integrating solar heat into your hot water system for safety.