Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Disconnect the 5-pin electrical plug connecting the air pressure switch and fan
Withdraw the fan assembly by pulling forwards from the top edge

Observation:

Inspect fan assembly, ensuring fan impellors are free from contamination and has unrestricted rotation.
Note:
Before reassembly check the integrity of all disturbed gaskets and seals and replace as necessary.