Asetek 645LT - pump is turning too fast and makes unhealthy sound

Hello everybody,

I proudly built my first PC, everything worked right away, although it wasn't fun in the DAN A4. I thought I would treat my i7 9700K to a water cooling system, namely the Asetek 645LT, which I connected to the MSI Z390i on "Pump Fan" on the mainboard.

According to Asetek, the pump should turn at 2800 RPM, but it doesn't work for me, it turns at about 5600-5700 RPM for me, which leads to a very unpleasant and loud buzzing sound, almost sounds like a coil whine, besides I can't imagine that this is healthy for the pump if the manufacturer's information is well below half.

My problem: I just can't get it set in this stupid BIOS. As soon as I turn the volts down, the system runs really super quietly and pleasantly until it has been shut down once, when restarting the starting current for the pump is probably not enough to move it to turn, because it doesn't move a millimeter and within a minute The CPU glows and the fan on the AIO turns completely on the wheel, but can't cool anything down because the pump doesn't even turn.

As soon as something above 6.6 V has been set in the BIOS, the pump starts up and can easily be reduced to 3.8-4 V again, at which it rotates at a quiet 2800-3000 RPM. Well, yes, but only until the system has been shut down completely, after which it won't start, unless I turn the volts up again in the BIOS and then down again, which is not a permanent solution.

I've already tried everything with DC, PWM or Auto. I've connected the pump to "SysFan" or to "CPU Fan", which I also try, my pump just doesn't want to run at the 2800 RPM specified by Asetek, mine I just turn the wheel to the full and after several days of research I am slowly getting a tinnitus: D

Does anyone of you have a similar problem or can you help me?

The following components were installed:

DAN Case A4
Intel i7 9700K
MSI Z390i
Asetek 645LT with Noctua NF-A9x14 PWM fan
Corsair SF600
Corsair Vengeance LPX 3000 with 32 GB
M.2 SSD from Crucial
Geforce GTX 1660 Super

Best regards from germany and stay healty


King of Cable Management
SFF Time
Bronze Supporter
Jan 2, 2019
Pumps have double the pole count of fans, so their rpm is often reported as double. Your pump is actually spinning at around 2800 rpm don't worry.
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Average Stuffer
Nov 12, 2020
Mine is also plugged into the AIO_PUMP port, QFan stuff on the BIOS doesn't let me modify it away from using full 100% even though I set it to DC (3 prong). I use Argus Monitor to set it once in windows. Also looks like 2800 is the minimum it will let me set the pump speed.

EDIT: 40% pump speed is 2800, which is silent, 100% pump speed is around 5800.


Lord of the Boards
Editorial Staff
Gold Supporter
May 9, 2015
Welcome to the forum ! The AIO_PUMP header's main difference is added amperage.