Your boiler has stopped working because a sensor that measures the temperature of the water heading to your radiators is sending an incorrect or broken signal.

The heating flow thermistor is too resistant.

What causes this fault?

This fault occurs when the main control board detects a signal from the heating sensor that is outside of its normal operating range. The most common reason is that the internal components of the sensor have degraded over time, causing it to report an impossible temperature, or there is a loose connection in the wiring leading back to the boiler's computer.