Your boiler has detected a fault with the internal sensor that monitors the temperature of your central heating water, causing the system to stop working as a safety precaution.

Central heating negative thermistor coefficient (NTC) sensor error

What causes this fault?

This fault occurs when the boiler's control board loses communication with the temperature sensor or receives an illogical reading that suggests the component has failed. The most common reason is that the internal sensor has suffered an electrical short or has aged to the point where it can no longer accurately track the heat of the water. In some cases, the issue is caused by loose or damaged wiring between the sensor and the main circuit board.