Most of the radiators in my house are not hot enough. Please will someone tell me how to top up the red small (header?!) unit linked to the megaflow tank. I was told by a plumber that the pressure should read at the '1' position on the meter and it's only at the quarter to position (on a conventional clock if you know what I mean). There are two taps to open/close which I tried but the dial didn't move. Any suggestions? Thanks.
