ESXi 5.5u2 reports a warning message (low speed) about a new [replaced] fan?

[nle]

Hi,

Hardware

• ESXi 5.5u2 box (a bit old by todays standards)
  • Supermicro X8ST3-F, Single Intel Core i7 / Xeon 55xx, 8 x SAS [Motherboard]
  • INTEL CORE I7 960 3.2GHZ 8MB S-1366 [CPU]
  • 6 x 4GB CORSAIR DDR3 XMS3 INTEL I7 1333MHZ [24GB RAM/Memory]
  • etc.

Story

• Dead cabinett fan.
  • ESXi showed a warning about slow fan speed (eventhough the fan is still, not moving).
• Buy an replacement fan (different brand, but same type)
• Shut down system. Install fan. Start up system.
  • Fan are connected to motherboard if anyone wondered.
• ESXi reports speed a tiny bit lower than the rest, but no warnings.
• 5 hours later ESXi reports slow fan (exactly the same as when the original fan died)
• The fan runs fine. Full speed. At least as fast as the other ones.

Why would ESXi suddenly report low fan speed even tough the fan runs fast and fine?
Is there any tricks to resolve this?
If I don't get ESXi to behave, can I somewhere remove/ignore the warning?

Thanks!

EDIT:
Looks like the fan speed varies, so I don't really know whats going on. It is connected with a tre-pin connection, and the fan is an Noctua NF-S12A FLX

 

[nle]

I figured this one out.

The problem fan is not the new fan, but an old one. It didn't even cross my mind since I got a fan warning a few hours after I installed the new one.

I guess I need to head out and by a second replacement.