Pressure Problem with Potteron Performa 24?

Hi everyone, The other day I bled my radiators, and later on there was no hot water or heating. This then led to a loud screeching noise from the boiler (which i imediately turned off.)

From what Ive read on here and other sites it sounds like a pressure problem, However I am crap with things like this and haven't been able to solve the problem myself.

There are 3 taps underneath the box, which I have taken a picture of here:

http://i8.photobucket.com/albums/a28/jagjagjag/boiler.jpg

At the moment I have switched the dial on the front panel to the off position.

if anybody could give me a step by step guide to fixing this that would be great. Our landlord is crap at fixing things like this and Im bl**dy freezing.

thanks.