Very high CPU idle temp(i7-8700K)



tried tapping/flicking the tubes to ensure no air is caught in the tube?
 


100C at Idle is ridiculous, sounds like your cooler is making poor contact with your CPU, check your installation. Remove and reinstall if needed.
 
The H100i V2 is powered by the fan header that it's connected to.

The fan header (CPU_FAN) that the H100i V2 connected to set to full power/100%. Do that first before you think that the pump is dead. If it's not getting the full 12V, then it won't operate properly. Additionally, if it has been working but hasn't been at 100%, it can cause the pump to die prematurely.