Set Appliance State:

Gas Off
Isolate Mains Power to appliance as per TOPs P4
Remove the burner door assembly c/w fan and gas valve assembly
Remove the silencer from fan assembly

Observation:

Visually inspect the silencer for any signs of damage,
restrictions or blockages.
Note.
1. Do NOT reassemble the appliance if the
visual inspections are satisfactory.
2. Always examine any seals or gaskets,
replacing where necessary.