Your boiler has detected that its temperature sensors are giving conflicting or incorrect readings, causing it to shut down for safety.

Fault:Flow/returnsensor Flow/returnNTCtemperaturedifferencetoogreat→flowand/orreturn temperaturesensordefective

What causes this fault?

This fault occurs when the boiler's control board notices that the temperatures reported by the flow and return sensors are too different from one another or are physically impossible. The most common reason is that one of the sensors has degraded and is sending an inaccurate electrical signal, but it can also be caused by a build-up of debris in the pipework affecting the heat transfer.