Your boiler has stopped working because it cannot correctly detect how much water is flowing through the system or what the temperature is.

Control / no flow thermistor fault

What causes this fault?

This fault occurs when the boiler's internal sensors provide conflicting or impossible temperature readings, making it unsafe for the unit to continue heating. The most common cause is a faulty flow thermistor that has failed electrically, or a significant lack of water circulation preventing the heat from moving away from the heat exchanger. In some cases, a communication error on the main circuit board can lead the boiler to incorrectly report this flow issue.