Question PC Rear Case Fan Issues


Apr 8, 2015
So I have a Lian Li Lancool 215 case, a Gigabyte Aorus x570 eilte mobo. the pc is built and runs perfect. however, if i unplug my monitors, peripherals etc... only leaving the psu plugged in and start my pc ALL fans work and run, then i plug in my peripherals and monitors and turn on the rear case fan does not spin at all, occasionally it will spin for half a second when i first switch the pc on, but it stops almost immediately. in the case the fans are attached to a panel that controls the LEDs etc, and ive swapped fans around to test if its the fan or the 4 pin connecter but all the other fans work in the connecters that the rear one was plugged in to. its fine for now but im worried that when i full load my pc or it gets stressed things will get too hot too fast and obviously that can cause many serious issues. any help or suggestions would be appreciated. the Sys Fan plug on my mobo is a 4 pin, the rear fan in question is a 3 pin, can i still put it in there to test ? and then manage it via bios? thanks in advance (i dont post on here often so i think ive posted this in the correct area)
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The only way temperature can go up "too fast" is if the heatsink of whatever the temperature of is going up "too fast" isn't properly installed since heatsinks will take a few minutes to reach steady state for whatever heat output and airflow are present.

If the rear fan won't spin regardless of what fan header it is plugged in but all of the other fans work as expected including on the fan header the rear fan won't work on, then the rear fan is most likely dead and you can simply put one of your other working fans in its place if any of them are the same size.

I only use three case fans in my PCs: two front intakes to take advantage of my cases' front air filters and the rear fan at its lowest possible speed mainly as a backup in case one of the intake fans fails. All other unused fan mounts and vent holes are taped shut for dust mitigation and constrain most airflow between the front intakes to rear exhaust path.