Your boiler has detected a fault with the sensor that monitors the water temperature returning to the unit, causing it to stop running for safety and efficiency.

Control mode: Return temperature sensor shorted out

What causes this fault?

This fault occurs when the sensor responsible for measuring the temperature of the water coming back from your radiators fails. The most common reason is an internal electrical failure within the sensor itself or moisture ingress that has damaged the connection, preventing the boiler from accurately monitoring the system's heat levels. Without this data, the boiler shuts down to prevent inaccurate firing and potential damage.