Happens on Librem 13v2 with PureOS and updated coreboot. Sometimes after short period of heavy CPU usage the fan stays on high speed even after the CPU is cold an idle. It stops when I put it sleep and wake up.
Does it happen to someone else? Any ideas how to investigate it further or prevent it to happen?
Librem 15v3, same here.
What is your coreboot version?
4.7-Purism-1
L13V2_COREBOOT_BIOS_SHA=“fe12dad83bfa76d56191db5a5091df9e07884aff0dc93e5b3a69ede4f2f4c199”
Is it 4.7-Purism-1 or 4.7-Purism-3
4.7-Purism-1 (post must be longer than 20 characters 
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There you go, you need to upgrade it to 4.7-Purism-3 (that’s the latest I think), and I think it will fix your issues.
It happens lot less after that upgrade, but it still happens sometimes.
Upgrade to 4.7-Purism-4. It fixes even more issues.
I have updated to 4.7-Purism-4 and so far that appears to have solved the overheating/shutdown problem described in other threads. However, occasionally after waking up from sleep the fan kicks into high gear and the CPU frequency (monitored via /proc/cpuinfo) appears to be held at the low end 400Mhz and does not increase when running CPU intensive tasks. A soft-restart does not seem to fix the issue, but after a power-off and boot-up from cold-start the CPU/fan begin working and scaling as expected again.
Same thing happens to me sometimes, but suspend and wake up helps.
Same here as well, with 4.7-Purism-4 on a librem15v3 - I get the occasional fan stuck at high speed after some suspend/restores.
CPU usage is low, sensors says core temperature is around 25°C which is very low and usually fans are quiet at this point.
Just like Honza, doing another suspend/resume cycle pushes the problem off and fans work normally afterwards, but it’s a mild annoyment (would say it happens about once a day or so, with 4-8 suspends a day, so not too often but often enough to be irritating when it does even if suspend/resume doesn’t take long)
Can confirm I’ve experienced the fan stuck on as well with 4.7-Purism-4
After the recent updates I have noticed the issue also.
I have noticed this as wel, with a Librem13V2, on PureOS. The cpu fan goes to maximum and will not stop.
There is no heightened cpu usage or a high temperature. I suspect it is a corner case in the thermal throttling in the firmware.
Reproduce:
Allow the laptop to go into sleep mode (I don’t know how long that is, guessing 10 minutes), the screen goes black and the wifi led turns off.
When you touch the mousepad or keyboard again, the screens turns on, showing the lock screen. If I type my password in quickly, I get the result as above; the cpu fan starts spinning at maximum.
Strangely, if I first mistype my password or just take my sweet time filling in my password, the cpu fan does not spin at maximum.
Temporary fix:
As suggested above by others, the temporary fix is to press the power button for 2 seconds, which causes the laptop to go back to sleep (since that is the default option in PureOS - Settings - Energy - Automatically go to pause)/ The cpu fan goes back to silent/off. When you unlock the lockscreen again; the cpu fan stays silent.
I have the exactly same issues after wake up from sleep. Sometimes, not always. Another sleep cycle fixes it but it is annoying…
Same issue here, with Librem 13v3 running PureOS; 4.7-Purism-4.
The temp. fix from warrenhead also usually works for me when plugged into AC (sleep, ensure AC, wake), but when on battery it doesn’t do so reliably. I’ve also found that when the fan is running post-wake on battery, the system becomes very laggy, with erratic CPU use (but nothing indicating where that use is coming from on the system monitor; all listed processes are low).
Hoping for a fix, as my primary use case for the Librem requires frequent sleep/wake when purely on battery.
I may have to add though that I have a pretty similar behavior on my Desktop PC as well from time to time. So it is possible that this may have a root cause outside of purism hard-/software direct influence?
Two days ago wanted to show some friends my new Librem. Starting it from sleep it directly went to full fan load as described above (didn’t start with the best impressions for the guys). Since then it is doing it reliably when waking from sleep. Might be, it is also draining the battery a bit quicker (beside the high noise-level i can only get rid of when completely shutting the laptop down + new start).
I have now upgraded my firmware to 4.8.1-Purism-2 and am still experiencing this issue. Periodically when waking from sleep the fan kicks into high gear and CPU frequency is held at 400Mhz. re-sleeping and waking resolves the issue.