Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Isolate and drain the domestic hot water circuit and remove the
electrical connection to the turbine
Remove the flow component assembly
Note:
Take care to ensure any water released from the flow component is
safely contained and cannot get on to the appliances electrics

Observation:

Examine the flow sensor/turbine, filter, flow regulator
and nozzles for signs of damage or blockage.