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).
Cheers,
Willem