I had a feeling something would go wrong with this loop.

My luck has been dreadful this time round.

The pump does seem totally primed. It sounds like it used to when the loop is totally bled, except for the odd whoosh of bubbles and the much higher vibration due to the res mounting system.

I really can't get the loop any simpler. I tried almost every single possible combination of components (some simply weren't possible due to tight bends), and this is the best I could do.

I might just go for another pump (two loops)... I saw the naked Alphacool D5 pump (no top) on sale here for about £60, and I guess I could stomach that considering I'll be returning my £40 flow sensor and won't be getting a replacement. It would also mean simpler tubing runs.

I did try Naekuh's suggestion, and antiacid's, but neither have done much. In fact, I think it would be a bad idea to simply tilt the case every other way, considering how unbelievably heavy it is. It's already developed a worrying flex...