Im currently running custom loop with i7-7700k @ 4.7-5.0GHz, GTX1080Ti SC and an EK240 Coolstream SE.
It's all being driven by the Pump from a Corsair, I think it was originally an H110i.
The pump is just temporary untill I get around to having a custom res. machined for...a more scalable pumping solution.
I write this to tell you that last week, when I received the 2nd (of 3
total) fittings package I bled and reconfigured my loop then had an airlock in that pump.
Its very lucky I was dealing with an open case design because, even full access including ability to invert and shake the pump, it took about 2 hours to clear that airlock!!
It gets noisy, rev's its guts out and is a total pain in the butt to get it fully primed.
During all that time it pumps barely a teaspoon of water over 5 seconds, but I must say, its designed never to be opened and it worked flawlessly for a year or so when sealed in it's original state (untill I pulled it apart
If yours has got an air bubble locked in there it could be a source of alot of your problems. For the cash and pain you could spare yoursel I would seriously recommend just replacing with a similar AIO unit, however FYI there is a fill/bleed port under the circuit board if you have some skills with tools and a soldering iron...
I highly recommend not to remove the screws that go are on the face where the copper interfaces with the CPU though, they are done up very tight, with quite shallow countersink heads, and made of poor material-I had an embarrisingly high destruction rate on those.
Asetek has the patent for a pump mounted to the cpu cooling block.....so pretty much all Corsair and similar styled AIO units are made by Asetek to the vendors performance and branding specifications.
Of course as a result of blanacing a brands variables such as, size, weight, cost, and ....bling-ness there are numerous differences in performance, but fairly minor I believe.