Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
DHW isolated and discharged
Remove the filter/venturi cartridge from the right hand hydro block

Observation:

Inspect the venturi/filter cartridge for damage, restrictions and corrosion. Pay particular attention to the venturi section highlighted below.
Note:
Care should be taken on refitting to ensure the cartridge is correctly orientated so that the filter opening is directly above the cold water inlet.
Incorrect positioning can adversely affect the DHW flow rate.