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

Flow Thermistor

What causes this fault?

This fault occurs when the internal sensor responsible for measuring the water temperature as it leaves the boiler fails or provides an unrealistic reading. The most common reason is that the sensor has physically degraded over time or a loose electrical connection has developed, preventing the control board from safely monitoring the heat levels.