Antec Kuhler H2O 920 with i7-3770K - high temps

- 2x (stock) 120mm front fans blowing in
- 1x (stock) 200mm side fan blowing in
- 1x 140mm fan on top (on the more to the front slot, not the back one) blowing out
- Water cooler radiator push-pull setup in back (both 120mm fans blowing out of the case)

Had an OC for a year (4,2 GHz with 100 base + 42 multiplier, fixed/manual Vcore voltage of 1,090 V as auto gave somewhat higher, I fine tuned to this and it ran 24 hours of Prime95 and already a year without crashing so I quess it's stable).
Idle temps are 40 degrees for all cores.

ASRock Z77 Extreme4 motherboard
ZOTAC GTX 670 AMP! Edition sitting on lower PCIe slot, no temperature problems (70-75 degrees at full load, 1170 MHz core, refitted screws with custom rings in between and reapplied TIM which lowered full load from 87 degrees to 74)
Corsair TX750 PSU
4x4 GB Corsair Vengeance RAM @ 1600 MHz
Corsair ForceGS 240 GB SSD
2x WD Blue 1 TB HDD

Around a week ago in Natural Selection 2, I noticed the GPU fans blowing really loud (NS2 [@max settings] uses more resources than BF4 [@ultra]). However, that was quite normal for me, as a year ago while in Furmark (400x300, 8x MSAA) testing it reached the same 85-87 degrees with loud fans, and I thought it was normal for such high OC.
However, I looked into my GPU thing, and I noticed when I pushed the cooling harder onto the chip itself, the temps went down 10 degrees instantly, so hence I refitted the screws with several of those small rings in between to tighten the screws, after this the GPU runs much cooler (even in Furmark it's around 75 degrees, 80 degrees after hours of testing).

CPU runs way too hot, and more important, I removed all OC settings (even reset BIOS settings to make sure, Vcore auto, Turbo on), running Prime95 still resulted in 80 to (after 20 minutes) up to 90 degrees in all cores.
This is of course not normal, as even the stock cooler could cool it down better with stock GHz.
I reapplied the part of the cooler on the CPU, fastened everything, reapplied Thermal Paste (AS5 again) (first cleaned with alcohol and one of those very fine cloth), nothing changed, still too hot.

Then I ran the ChillControl software, the utility and driver of the H2O 920 cooler.
Pump speed, since the first time I booted up 1,5 years ago, is still 3100 RPM (over the max), and sits there +-100. Fan speed behaves normally (600-700 RMP while idle, ramps up when liquid gets hotter). Made sure the fans were working, I could feel the blow coming out.
When I turn fan settings on "Extreme" (100% both fans on) while being extremely loud, cools the liquid down slightly (from 52 degrees back to 45 of the liquid temp) and then stops it from increasing for a while, then temps sit around 47 degrees (liquid temp). Core temps are not (or barely, unseen by the nature of CPU cores going +- up to 10 degrees in a second, up and down) affected.

What I noticed is that I think the warmth does not stay in the CPU, as when running Prime95 (all testing done in Stock GHz clock), I can feel the thing on the CPU getting warmer.
The liquid temperature, however, this is one of the things I could find nothing about, increases at a great speed. A minute after running P95, liquid temps rise 0,2 degrees every second, in 3 minutes the liquid temp goes up from 29 degrees to 52 degrees and keeps increasing. One of the tubes (I presume it's the one leading liquid from the CPU to the radiator) gets really hot, other tube feels cold. I can feel quite some warmth coming out of the backside over the radiator as well, so I have somewhat the feeling the radiator cools properly.
Now I don't know if something like this could happen if the pump stopped working.
I don't see any leakages.

Also, don't rule out any of the options what I have mentioned previously (like it still could be that the radiator is not cooling properly for example), as I have not done an extremely in depth research, and I don't know for each part if it's normal (like the liquid getting hot).