Blocked Anode Fan (reference 2 image).

Check if the Anode Fan is not blocked. Ensure that the Anode Fan can turn freely.

Damaged wire unit (reference 1 & 5 image).

Check if the wire unit of the Anode Fan is not damaged. Repair if possible, otherwise replace with new one.

Malfunction Fan Control board.

Replace the Fan Control board. See service manual chapter "Replacement of a Card Cage board".

Anode fan (reference 1 image) end of life.

Replace the Anode Fan. See service manual chapter "Replacement of the Anode fan".