In my case the CPU AMD A6 9220 has 2 Core for CPU, 3 Core VGA on one single chip die as its an APU, AMD Radeon R4, it maybe a coincidence my CPU becomes fully loaded (possibly runtimebroker) and how its related but one thing I am certain of in my case its
graphics driver related.
This is also worth a try and something which ties in with the other guys post about removing certain apps, if you go into your start menu and turn OFF the live tiles such 'news', 'money', xbox and all live tiles etc you should see a jump in the performance
of the laptop.
The live tiles put a huge burdon on the graphics, runtimebroker.exe monitors apps that are not behaving properly so this ties in with.... graphics driver not responding correctly=app not properly responding=runtimebroker.exe error message and high CPU\GPU
load. This happens if you click settings in start menu only and as you said not if you access settings through another method, only through the start menu where the live tiles sit.
The live tiles can easily be turned back on, just right click and 'more' turn off\on'
Worth a try im sure