Your boiler's internal temperature sensor has stopped sending a reliable signal, which means the system cannot safely monitor how hot the water is for your radiators.

Central Heating NTC Fault

What causes this fault?

This fault occurs when the thermistor, a small sensor that monitors water temperature, fails or provides an incorrect electrical reading to the boiler's control board. The most common reason is internal degradation over time or loose wiring connections, which prevents the boiler from knowing when to safely turn the burner on or off.