4.2 GHz is not 0%, it's 20%. The H70 is an old and too small, so I'm surprised you even get to 4.2 GHz with it. My 4770K hits about 83C running Prime95 AVX at 4.3 GHz with a Phanteks PH-TC14PE air cooler.
I would suggest you replace the CPU if you can, and also switch to the H110 or a high-performance air cooler (twin tower design).