I haven't been able to find the answer to this anywhere else online but
I've got a problem with my Sime Friendly Format 80E water boiler.

The pressure's dropped to about 0.3-0.5 instead of the 1.0 it usually
hovers around.

I have a filling loop to top it up, so was going to try that before
calling an engineer, but it's been so long since I've needed to use it
I've forgotten what to do next.

I've connected it up, but there's a nut or a screw near each connection
that can be turned, but the nut by the connection where the pipe is hot
just leaks water if I unscrew it, and the screw by the connection where
the pipe is cold just won't turn*. I thought that was the one I used to
turn before but it's stiff as a board.

In this page:
http://www.diynot.com/forums/viewtopic.php?t=38904

my filling loop looks like the one on the right-hand picture but I
still don't know what to turn on the boiler to make the water exchange
happen. I'm sure it was just one of the two things I mentioned as
opposed to both.

(*Actually, I managed to turn (anticlockwise) the very stiff screw,
close to the cold pipe, but then that started leaking water as well so
neither seem like the right thing and they're the only two things I can
turn in the vicinity)

Does anyone know, please? TIA,

Dom