Your boiler has lost connection with a temperature sensor, meaning it cannot safely monitor the heat of the water going to your radiators.

Central heating NTC unplugged

What causes this fault?

This fault occurs when the boiler's internal computer can no longer detect a signal from the temperature sensors located on the main pipes. The most common reason is that the sensor has developed a hardware failure or the electrical wiring connecting it to the main control board has become loose or damaged. Without this connection, the boiler shuts down as a safety precaution because it cannot tell if the water is becoming dangerously hot.