Your boiler has detected a problem with the internal sensor that monitors the temperature of your heating water, meaning the system cannot run safely.

Central heating thermistor/wiring fault

What causes this fault?

This fault occurs when the boiler's control board loses communication with the sensor that measures the temperature of the water in your radiators. The most common reason is that the sensor has physically failed or 'drifted' out of its correct electrical range, but it can also be caused by loose or corroded wiring connections between the sensor and the main circuit board.