Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4

Observation:

Inspect the venturi, it should be clear and unrestricted.
Notes:
1. There are different designs of venturi but the test remains the same.
2. It should be possible to inspect the venturi in situ but if it is deemed necessary then the fan can be removed to gain better access to it.
3. If the fan was removed for this test and the venturi is satisfactory do not refit it at this stage.