Your boiler has lost communication with the sensor that monitors water returning from your radiators, often causing the system to stop working as a safety precaution.

Return sensor open circuit – check connections to return sensor are in place

What causes this fault?

This fault occurs when the boiler's main control board can no longer read the temperature of the water coming back from your radiators. The most common reason is that the internal sensor has developed an electrical failure or the connecting wires have become loose or damaged. Because the boiler cannot monitor the water temperature accurately, it shuts down to prevent the system from overheating.