This issue is described here: http://www.intel.com/support/motherboards/desktop/sb/CS-034326.htm. There is a link on that page where you can submit an email request for a thermal pad to install inside the NUC chassis that will help solve the overheating issue.
Ok, so I've installed the thermal pad but unfortunately I'm still experiencing lock-ups. However, it's useful to know that it could be the hard drive causing the problem. For the record I'm using a Crucial CT128M4SSD3. There's a good chance these may run hotter than an Intel equivalent. So, it's time to try an Intel drive next.
I'm having a similar issue as stated above: After a couple of minutes (from ½ to about 3 minutes) the computer freezes.
Tested, with the same results:
1. Standing in BIOS (v42)
2. Running Ubuntu Linux in terminal mode with less than 1% CPU usage
3. Running Ubuntu Linux in KDE, Gnome, Unity and Xfce
4. Running USB-bootable drive without HDD
5. Running Memory tests (on Ubuntu Installation disc)
6. All above both with LAN, USB-WLAN and no Network device connected
7. Running Ubuntu (Unity) with no screen connected, after a couple of minutes connecting a screen
8. All different possible "run CPU fan all time" to "run CPU fan as little as possible" settings in BIOS
BIOS is really showing some interesting CPU temperatures - jumping between 75 and 100 seemingly randomly.
Is there some type of suggestion for solving this - which is not "attach a thermal pad between the SSD and the chassi" I would be glad to try it out.
See my reply above. Because of the performance during use without a SSD installed it's pointing towards either the temperature sensor, CPU-mounting (guessing it's directly soldered: probably not) or mounting of cooler package.
This is today a useless piece of computer, and because heating related issues are so plentiful makes me reluctant to recommend this platform to anyone as we speak.
Since you see the issue even without an SSD in the system, it sounds like you do have a defective unit that needs to be replaced. The quickest way to get a replacement would be through your place of purchase. If that is not possible, you can send an email to Intel Customer Support (http://www.intel.com/support/mailform/desktop/nuc/emailsupport.htm) for further assistance.
When requesting warranty replacement, you will need to include the following information:
Serial number and SA Number (found on a barcode label on the bottom of the chassis)
Please also reference this community thread for the warranty agent to review.
An update: after doing some further research I didn't end up buying an Intel hard drive as it didn't look like it would solve the overheating issue. Instead, I decided to swap out the original Intel case with a Silverstone SST-PT14B-H2. Having taken the motherboard out of the original case and comparing the two the Silverstone appears to be more efficient at cooling in terms of the heatsink, the fan is much larger, and the overall airflow seems better. I've only had it just about a week so it's still early days but I've tested it out with lots of browser based video streaming and haven't had any problems so far. The temperature readings in SpeedFan look much better. In addition, I think the thermal pad was actually making the overheating situation worse.
As a side point, since I was having trouble finding any specific instructions on how to remove the motherboard from the case (the videos I found seemed to skip the actual removal) I thought I'd share my experience with this. I just needed to remove the two screws that secure the board to the case (these are the slightly offset ones from the main screws which hold the cover on). Next, with a plastic scribe or flat blade screwdriver, on the edge of the case which has slightly more of a gap (away from the ports), dig underneath the motherboard and start gently levering the board upwards moving towards the corner and round until you get a good grip on it. You will feel a bit of resistance but eventually the board will pop out from the case. From there you just need to unplug the fan and remove the original heatsink.