Your boiler has detected a faulty internal temperature sensor, which means it cannot accurately measure how hot the water is and has stopped running for safety.

CH flow NTC sensor defective.

What causes this fault?

This fault occurs when the sensor responsible for monitoring the temperature of the water leaving your boiler fails or sends an incorrect signal. The most common reason is the electrical component inside the sensor wearing out over time, though it can also be caused by corroded wiring connections or a build-up of heat that has damaged the sensor’s sensitivity.