Hello Robert, thank you very much for contacting us.
This situation has been escalated to our engineering team. Please check the following thread for additional information NUC DN2820FYKH: WARNING: Processor thermal trip at boot
With my 2820, I noticed the mainboard (probably CPU ambient) and memory temperature are measured.
Possibly it's the memory module that is causing the thermal trip warning/error?
Also, I noticed a change in the thermal monitoring in newer BIOS versions.
Possibly it is a good thing to upgrade the BIOS, as the stock/shipped one seems a bit buggy.
Careful though, I ran into issues with the newer BIOS versions on the 2820 and USB UEFI/GPT booting (check my topic for details; https://communities.intel.com/message/248031#248031).
I'm using a memory module which is on the compatibility list (and works fine in a laptop, for that matter). On the disk, I'm using MBR, not GPT. The machine works fine, I'm using it as a HTPC. But after every reboot, even from a cold boot, it displays the thermal warning.
I got the same error tested the device with Prime95 and other benchmarks no problems with temperature so far. So still think this is a BIOS Bug