Isn't the h100i gtx getting its power from the 4 pin on the motherboard and not from a PSU connector?! If so then Check if the fan header you have connected is at full speed and not at pwm or DC operation at it would not deliver the necessary power to the pump and the fans!
Second check if the pump is making any grind noise, even that was a issue with the h100i and not so common with the h100i gtx.
"Optional Extra Step
While the H100i GTX is designed to be as easy to use as possible, you may need to disable fan control on the CPU_FAN header in your motherboard’s BIOS. Consult your motherboard’s user manual for information on how."
From how to install
a h100i gtx