One of the two wire units (reference 1 image) of the Heat Exchanger fans (reference 2 image) is disconnected.

Pull out the Liquid Cooling assembly (reservoir, pump and heat exchanger) from the projector until you see the fan connections. Check if both fans are connected. Ensure the wire units are hidden between the fans and thus not obstruct the air flow of the fans.

Wire unit of the fan units (reference 5 image) disconnected from the Signal Backplane.

Remove the front cover and front dust filter from the projector and check if the wire unit (reference 5 image) is inserted in the Signal Backplane.

Blocked fan (reference 2 image).

Unblock the fan. Ensure that the fan can turn freely.

Damaged wire unit.

Check if the wire unit of the 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".

Fan end of life.

Replace the fan. See service manual chapter "Replacement of the Heat Exchanger fans".