Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Isolate the cold mains to the appliance and discharge DHW circuit
Remove the flow turbine assembly from the hydroblock

Observation:

Inspect the condition of the turbine, filter and flow limiter if fitted to ensure there are no restrictions or blockages.
Note:
Not all appliances incorporate a flow limiter. Graphics below do not show the flow limiter.