Your boiler has detected an electrical fault in the part that measures the temperature of the water being sent to your radiators, which prevents it from heating properly.

Short circuit on flow sensor

What causes this fault?

This fault occurs when the boiler's internal sensor responsible for tracking the temperature of the water leaving the unit fails electrically. It is usually caused by the sensor's internal wiring failing over time or moisture getting into the electrical connections, which prevents the boiler from safely knowing how hot the water is. Because the system can no longer regulate its heat output, it shuts down to prevent overheating.