Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Remove the venturi from the gas manifold

Observation:

Inspect for blockages or damage particularly around the drilled holes around the bottom of the component.
Note:
1. Before reassembly check the integrity of all disturbed gaskets and seals and replace as necessary.
2. Upon reassembly all disturbed joints should be checked for gas tightness.