Your boiler has detected a problem with the internal sensor that monitors the temperature of the water as it leaves the unit, causing the system to shut down as a safety precaution.

Flow Thermistor Fault

What causes this fault?

This fault occurs when the boiler's control board can no longer get an accurate reading from the sensor that monitors hot water temperature. The most common reason is that the sensor has physically failed or developed an electrical short, though loose or damaged wiring between the sensor and the main board can also cause the connection to drop out.