Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Gain access to PCB
Remove connector to flow sensor
Pull X8 back slightly to expose test pins

Measurement:

Check for continuity (zero resistance) of each of the
3 wires running between X8 and the disconnected plug.
Black = X8 Pin 8.
Blue = X8 Pin 9.
Red = X8 Pin 10.
Inspect harness and connectors for good overall condition.
Note:
Wires may be multicoloured.