I put together a PC yesterday, which went smoothly up until I loaded up Open Hardware Monitor to check the temperatures of each core on the CPU.
The build used the following:
- i7-8700k CPU
- ASRock Z370 Extreme4 motherboard
- Cryorig H7 CPU cooler with Arctic Silver 5 thermal compound
While cores 1-3 and 5-6 are reading low temperatures at rest - 25-26 degrees Celsius, core 4 is reading 108-109 degrees Celsius.
Core 4 is also under little to no load while reaching these temperatures. My BIOS also reports a CPU temperature of ~39.9 degrees Celsius, which is consistent with what I see in Open Hardware Monitor upon starting Windows.
I thought I may have applied the thermal compound incorrectly, so I removed the CPU cooler and remounted it, applying the compound in a different way (I spread it with a card the first time, this time I just put a small dollop in the center of the CPU's heat spreader and mounted the cooler facing the other way since I'd mounted it backward the first time), but the problem persists with almost exactly the same temperatures on all cores. The CPU cooler's fan is not increasing its speed despite the high temperature on core 4, either, though I'm not sure if it should.
After reading some answers, I've also tightened the screws on the cooler's backplate. There has been no change in the temperature readings.
What could be causing this, and where is the problem likely to be? What can I do to fix it?