Your boiler has detected that the temperature sensors are giving unusual readings, likely because they are loose or have been installed on the wrong pipes.

Fault: NTCs fitted incorrectly Flow/return temperature sensors returning incorrect/implausible values. Check: Flow/return temperature sensor (correct thermal connection).

What causes this fault?

This fault occurs when the boiler's control board detects that the temperature sensors are not sending consistent or logical readings. The most common reason is that the sensors have vibrated loose from the internal pipes or were accidentally clipped onto the wrong ones during a recent repair. Because the boiler cannot accurately track how hot the water is, it shuts down for safety.