Your boiler has detected a problem with the internal sensor that monitors the temperature of the water heading to your radiators, causing the system to shut down for safety.

CH flow NTC sensor defective (short or open circuit)

What causes this fault?

This fault occurs when the electrical connection to the temperature sensor on the main heating pipe becomes unstable or fails completely. The most common reason is that the sensor itself has developed an internal electrical fault or the wiring has become loose or damaged over time, preventing the boiler from safely monitoring heat levels.