Brand new aftermarket CPU cooler won't start without a nudge

I have had problems with my CPU fan.
I had a Noctua NF-A15 top of the line cpu cooler that suddenly stopped working on its own. About 5 minutes after booting the PC it started moving slightly and when i nudged it it started working normaly. I was sure the fan broke down so i bought a brand new, same model, Noctua fan. After replacing it nothing changed, except my wallet being 25€ lighter. The problem wasnt that bad untill it recently started to randomly stop working in the middle of gaming. Which i only noticed after checking the temps that went from 60 to 80+ degrees. I have probably checked all the solved threads with the same problem, but they almost always solved the problem with a new fan. Well, I now have 2 perfectly working 25€ Noctua fans and still no solution.
Pls help, ty
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  1. Concerning, but possible it's the CPUFan Header on the motherboard that's defective. How many times have people 'nudged'/whacked something only for it to assume normal function?

    I would suggest you hard-wire your CPU fan to your PSU initially (you'll likely still need something attached to the fan header for the system to boot). You'll likely need a molex adaptor in order to do so, but at least you can test that the fans themselves are fully operational - while also cooling your CPU. The fans will run at full speed when connected to the PSU though, so it's very much a short-term solution.

    If your CPU fan header is defective, there's really not much you can do about that, other than a new motherboard.
  2. One possibility is that the CPU_FAN control system is set to a minimum voltage that is too low. This would allow the fan to fail to start from stopped, and to stall and fail to re-start.

    BUT this should only happen with a control system operating in Voltage Control Mode, and you have a PWM fan. So there are three possibilities. Check each of these.
    1. That Noctua fan comes with little adapters you can plug into its supply wiring called "Low Noise Adapters". These are merely resistors that drop the supply voltage so the fan runs slower (and hence quieter). But for any fan under automatic control by a mobo port, you should NEVER use these! The automatic control system will ensure the fan runs only as fast as necessary. So IF you have those items installed in the fan hook-up, remove them.
    2. Go into BIOS Setup (you don't tell us your exact mobo, so I can't point to exactly where your manual covers this) to where you configure your CPU_FAN port. First check its control mode. Usually you have choices like "Default", "Auto", "PWM", "Voltage Control" or "DC Mode". Since you have a PWM fan, make sure this is set to PWM Mode.
    3. Again in the fan configuration settings, see if there is a setting for minimum speed or minimum voltage. You could raise that so the fan does not stall.
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