Your boiler has detected that its temperature sensors are giving conflicting readings or have failed, which has caused the system to stop working for safety.

NTC fault

What causes this fault?

This fault occurs when the boiler's control board detects a significant temperature difference between the flow and return pipes that doesn't make sense logically. The most common reason is that one of the internal sensors has either become uncalibrated or has failed completely, leading the boiler to shut down to prevent overheating. In some cases, it can also be caused by a faulty wiring connection between these sensors and the main circuit board.