How do you check the CPU temperature? The Corsair Link utility used to configure the H80i by default shows the Coolant (liquid) temperature. If you are checking this then there is a possibility that the cooler is not properly mounted on the CPU. You can verify this by checking the actual CPU temperature (available within Corsair Link as a separate configurable monitoring parameter or another utility like Speccy or RealTemp). If you see a large difference in temperatures of the coolant and the CPU then it means that you may either need to tighten the cooler block or remove the cooling block and remount with new thermal grease.
I'm not sure if you are aware of this (I was not, when I first used my H80i), but by default Corsair Link uses the coolant temperature to vary its radiator fan speed. You can change that to make it so that the radiator fan speed varies based on the CPU temperature, which I think makes more sense.
Hope this helps and all the best!