Your boiler has detected an electrical fault with the internal sensor that monitors the water temperature leaving the unit, causing it to shut down for safety.

Flow NTC short circuit. NTC defective, short circuit in cable harness, cable/casing short cut

What causes this fault?

This fault occurs when the electrical connection to the flow sensor is interrupted, usually by a short circuit in the sensor itself or the internal wiring. This is often caused by moisture ingress from a small leak or natural wear and tear to the electrical components over time. Because the boiler can no longer safely track how hot the water is, it shuts down to prevent overheating.