Your boiler has detected an issue with the sensor that monitors the water temperature, causing the system to shut down as a safety precaution.

Primary temperature sensor (NTC) fault

What causes this fault?

This fault occurs when the sensor responsible for monitoring the heat of the water inside the boiler fails or sends an incorrect signal. The most common reason is that the sensor has physically degraded over time or developed an electrical short, meaning the boiler can no longer safely track temperature. Because the system doesn't know how hot the water is, it shuts down to prevent the unit from overheating.