Help decipher central heating pipework and valves (with pictures)

schriss

My water pressure is low when I turn the boiler off, about 0.2 bar. But when I turn boiler on, it goes up to about 1.2 bar.
Anyway, I was looking for a filling loop or any kind of valves/connectors under and around the boiler, but there is definitely nothing there. I looked around the house and so far have not found any filling loop or valve.
Now, in this small area where the hot water tank and the expansion vessel are located, I do see some valves. But they all seem to be open. There is one there, on the first picture top-left, that appears to be one-way valve with an arrow on it pointing down, there is also red (fully open) valve just before it. On that non-return valve there seem to be a square screw which I did not touch. The pipe above the valves seem cold, but it gets warmer and warmer down below the valves. What could that valve be?

(Can't post links, replace with https)

h..ps://drive.google.com/file/d/0B6-LrN8njTN2aDM1Y19JLVpxeVE/view?usp=sharing

h..ps://drive.google.com/file/d/0B6-LrN8njTN2UHNpcHRsRXdSSDg/view?usp=sharing

h..ps://drive.google.com/file/d/0B6-LrN8njTN2TU13T1pZMTVwRHM/view?usp=sharing

wait4me

Might be better in Plumbing forum - the Mods might move it for you.