Your boiler has lost its ability to measure the temperature of the water coming back from your radiators, often resulting in the system shutting down for safety.

Return Thermistor Fault

What causes this fault?

This fault occurs when the sensor responsible for monitoring the temperature of the water returning to the boiler begins sending incorrect data or stops communicating entirely. The most common reason is that the internal components of the thermistor have degraded over time or a wire has shaken loose, preventing the boiler from safely managing its heat output.