Ok, so I found time this evening to strip the PC down, drain the system, test the pumps, remove the motherboard, remount the block, re-install everything, prime the watercooling, and get it all back up and running.
Pump
This turns out to be operating fine. I performed the test, as advised by pastymuncher. Calculated the flow rate to what OcUK say it should be and it is bang on. As such, we must assume that the pump is working as it should. I did, for a laugh, manage to hook up my old eheim 1046, which actually has a better flow rate, but is more cumbersome, noisy and intrusive that the XSPC 750, so it's not going to be used.
CPU/Block
I bled the system, and removed the CPU block. The thermal paste had spread evenly over the block and the IHS. Removed the motherboard from the chassis, cleaned everything, and remounted the block. Was so much easier with the motherboard being flat on my desk. See attached pictures, showing the mountings once done...
and the other side...
Then tightened the lower bolts, til they would not turn any more...
Big picture, hence the spoiler window...
I followed the previous instructions, so tightened 2 corners at a time, until they were all pretty tight, and then finished them off individually.
Re-installed the motherboard, etc. etc. Re-plumbed the loop, re-filled it, bled it once again (tilted the chassis 90 degrees each way, to ensure all the air was out of the system). Leak tested and then re-booted PC.
So, have the temperatures improved?
No, not really, they are still where they were before. I suppose they are marginally better, but nothing to get excited about. Screen of latest burn test below..
Yes, we still have the weird Core 0 reading. That has always been there, so I am guessing I have a screwy CPU.
I am thinking I may stop there. The temps never get this high under "normal" use, so I am not concerned that my CPU is going to overheat etc. Maybe I am just unlucky in having a hot CPU, who knows. The PC is quieter and much nicer to live with than with the old air cooling system, so at least there is that.
If anyone can think of anything further, by all means share.
Thnx for reading.