Your boiler's internal sensor that monitors the temperature of the water returning to the unit has stopped communicating correctly, causing the system to shutdown for safety.

Return sensor error – t-sensor damaged, short circuited, sensor damaged or wiring broken

What causes this fault?

This fault occurs when the boiler's internal computer loses the ability to read the temperature of the water coming back from your radiators. This is usually caused by the return sensor failing internally due to age or heat stress, or a loose connection in the wiring that prevents the signal from reaching the main control board.