I have an Optiplex 3060 MFF with i3-8100T at home for private administrative use. It is just out of warranty.

Since a few days it randomly powers off (no Windows shutdown, just boom.. off). When I Power it on again it starts up with a warning: "Dell SupportAssist has detected a a failing component etc."

Error code: 2000-0711

Thermal - Thermal trip detected. (previous Desktop Thermal Failure) Alert! Previous shutdown due to thermal event.

Using the QR-code I get a page with advice to check the fan and vents and update my BIOS. Unfortunately no details about which component exceeded a thermal threshold.

The fan is running fine, all vents and cpu-cooler fins are clean as new. My BIOS is the latest: 1.9.1.

The weird thing is: until now it only occurred (about 10 times in 3 days) when the system was idling or doing very light tasks. It passed the preboot diagnostic test several times, it passes the short and long SupportAssist tests. I can let it run at 100% CPU for an hour using Prime95 and it passed PassMark Burn-in test several times. During these tests I let HWInfo64 monitor the thermal sensors. CPU peaked at 75 °C. The hottest part is the VR VCC that peaked at 83 °C.

Any suggestions about what could be the problem?