Set Appliance State:

Gas Off
Isolate Mains Power to appliance as per TOPs P4
Isolate and drain DHW supply to boiler
Remove Gas Valve
Remove DHW flow switch

Observation:

Inspect the DHW flow restrictor for blockages or damage.
Note:
Restrictor can be removed for easier inspection using circlip pliers.
Ensure all disturbed gas joints are checked for gas tightness on reassembly.