Can't figure out how to repressurise boiler

I have a Vokera Mynute 28e boiler that's on its last legs but I'm trying to eke it out until the summer. The pressure keeps dropping and last time I called someone out they said that it was possible to repressurise it myself by turning one of the taps. Unfortunately I didn't get them to actually show me and I have just realised it's not that obvious and despite trawling Google and youTube I can't find someone with the same set-up that I have. I've tried a few things already to no avail so I'm attaching a pic of the pipes in the hope that someone can help.

I've tried to turn the red tap but it only turns about 20 degrees and seems to have to effect. I've turned the inside bit of the black one (spot the novice plumber) below the guage and again nothing.

I've just realised as a newbie I'm not allowed post a pic yet. Perhaps someone can help anyway?

Thanks!