Your boiler has stopped working because a sensor that measures the temperature of the water leaving the unit has stopped sending a reliable signal.

Your flow NTC has developed a fault.

What causes this fault?

This fault occurs when the internal sensor responsible for monitoring the heat of the water leaving the boiler fails to send a consistent electrical signal to the main control board. The most common reason is that the sensor has either suffered an internal electrical failure or developed a loose connection, causing the boiler to shut down as a safety precaution. Over time, constant changes in temperature can wear these components down until they eventually fail to report accurately.