Reason for fan to stay on or maximum level ?

[hhhd1]

Trying to debug a laptop that I do not have access to, and want to buy.

The current owner is complaining that "the fan stays on".

what is the possibility that this is a MB issue, and not just needing a BIOS update + TPFanControl ?

is it possible for a fuse or MB chip to cause the fan to run constantly at level 7 or level 64 ,.. or any other level ?
what is the probability of that happening ?

[brchan]

It probably has a dust clogged heatsink and fan.

Never encountered an issue with the MB causing fan to always stay on. With performance mode set on fan in bios, it should probably still disengage at idle.

[WarMachine]

Hello hhhd1,

What is the laptop you're trying to fix ?
I've read that the T420s sometimes has a fan which is very noisy. I own a T420s and I've heard that the fan makes much noise than the ones of my previous Thinkpads. I've upgraded the BIOS and installed TPFancontrol, the result is better. I install this software on every Thinkpad I have, and I've been very happy with it.
For the T420s, I've read too that changing the fan can stop the problem. But it's always better, according to me, to try to fix by configuration and BIOS upgrade before replacing the components. It's always cheaper ! And before that, you can also try a little cleaning with a bottle of air duster, or after the disassembly of the laptop.

Have a good night,

W.