Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Isolate and drain the mains water supply
Unclip and remove the hall sensor from the cartridge assembly
Remove the flow turbine cartridge from the hydroblock (18mm)

Observation:

Visually inspect the turbine and its blades it should be smooth, unpitted and clean / unrestricted as shown in the "working turbine" example below.
It should also be free to turn.