Oh sorry I thought I mentioned it. Its under AUXTIN. CoreTemp temps are fine.
Hey Kaizer - I'm in the same boat - I just built a computer - using the ASROCK 870 Extreme 3 Mobo too. The same thing happens to me. Currently the AUXTIN section, under Temperatures, says 124 C (255 F) - Obviously something is wrong with the program.
I wonder if it has something to with the fact the 870 doesn't have gpu built it and HWmonitor is trying to take a sensor reading of something that isn't there...? Dunno