Question Neither CPU fan nor System fan spin

Aug 23, 2021
I bought a frankenstien machine and thought Id try to make it work. Neither fan will spin* and I cant proceed to Windows because I get the "fan not operating" error.

HP Pavillion with Berks motherboard
i7 9700 95w (I discovered this motherboard only supports up to 65w CPU, but I hope this is just a bottleneck issue)
Foxconn system fan 0.4A
Noctua fan with heatsink 0.21A
** I purchased a be quiet system fan 0.32A to troubleshoot
16g ram (2x8)
500g HDD
HP 400W power supply

Here are some things I noticed.
  1. If everything is hooked up correctly, BIOS says both fans are N/A.
  2. If I plug the Noctua to either the system fan bus or CPU bus AND no other fan, BIOS will show both fans at around 1500 RPM (but only after I give it a little push to get started). This happens even though only 1 fan is plugged in.
  3. If I plug either of the other fans into either of the bus, BIOS will not recognize them at all.
  4. HP BIOS does not allow fan control, that I can find anyway.
Is it possible that there is not enough power and this is why the Noctua will spin (barely) but not the others?
Is it possible that there is not enough power and this is why the Noctua will spin (barely) but not the others?
if PWM mode with a 4-pin fan;
if it doesn't start moving usually it is because the header was not supplying a fast enough start RPM to activate the fan.
usually it would need to be set ~20% for lowest temperature.

if DC 100% mode;
it may be an issue with the fan because it should be supplied 100% power from the start.

check for any motherboard BIOS updates.
if it's a proprietary Dell board look at the support pages for the original model desktop that it came in.

also try resetting BIOS optimized defaults and see if anything regarding the fan support changes.


I'd say it is likely the fan headers are operating in 3-pin Mode and controlling fan speed by reducing voltage. It appears it reduces that too much, and the fans are stalling. You say there is no option in BIOS Setup tp set fan speeds at all. If so, you will have only one choice. Get adapters so you can power each fan directly from a PSU power output - 4-pin Molex or SATA. HOWEVER, you still have the refusal to run with "no fans".

So, BEFORE changing how fans are connected, set it up with the Noctua pluggedinto the CPU_FAN header so you CAN get it to boot into BIOS Setup. Look very closely at the CPU_FAN configuration details. I(t may allow you only yo run the fan ot not. IF you can find a setting to IGNORE this fan, tell it to do that. This wasy it will NOT try to seee the CPU_FAN speed and will not worry about no speed signal. THEN you can change to powering the fan from the PSU and not from the CPU_FAN header.

You MIGHT have to do something similar for the SYS_FAN header. Most systems may warn you if that fan fails, but will not refuse to start just becasue they get no SYS_FAN speed signal.