issue with xspc x20 pump

[dazzyboy10]

Hi guys. I just purchased the maximus v formula board for my watercooled system and wanted to incorporate the onboard thermo block into it. The problem I'm facing is that when its turned on, there seems to to be a huge air bubble in the tubing, coming directly from the the heat sink. I am wondering if the pump isnt strong enough to get the fluid moving as it goes from pump to top 240 Rad, then to CPU block, then bottom of thermo heat sink, and from top of heat sink to gpu block, then into a font 120 Rad and back to the pump. The fluid just seems to trickle through the tubing from the top of the heat sink. The pump I have is the older acrylic xspc x20 750 pump/res combo. Should I be looking at a stronger pump or maybe a desperate res/pump.

Thanks for any help guys