Your boiler has stopped working because it cannot correctly measure the temperature of the water returning to the unit.

Return temperature sensor failed

What causes this fault?

This fault occurs when the internal electronic sensor responsible for monitoring the water coming back into the boiler becomes damaged or loses its connection. Over time, heat stress or moisture can cause the sensor to degrade, preventing it from sending a reliable signal to the main control board. Without this vital temperature data, the boiler shuts down as a safety precaution to prevent internal overheating.