How do I raise the pressure on a worcester Junior 28i Boiler?

I am renting a flat with a Worcester Junior 28I boiler and recently the pressure has dropped below 1 and will not rise above 1 (bar) and the red oval warning light comes on flashing fast. I can get hot water by holding the warning light/button for about 5 seconds until it switches off, switching the boiler onto "on", waiting for the pressure to reach 1 bar and then using the hot water. After about 15 minutes of the boiler being on I can turn it off on the control pannel and if continuous use is being made of the hot water, I can get hot water without the warning light coming back on.

I have been told that I need to repressurise the boiler and have read other internet posts on this. They all say that I need to turn the stop tap attached to the metal hose to run cold water into the boiler. I turned the only tap (red in colour) that doesn't require some sort of metal key (which I dont have) (the tap is also attached to a metal weave flexible tube encased in clear plastic) and the only result was a very fast depressurisation and a hissing noise like air escaping. This red tap is located on the upper left hand side of the boiler. I can also find a black switch which moves 180 degrees through 3 different settings marked I II and III . It is set on III and has always been. Turning it to II or I results in a slow drop in pressure or the boiler warning light flashing fast. I cant find any other hand movable buttons or taps. The only visible taps are 5 metal taps arrayed along the front underside of the boiler marked with (left to right) 4 vertical lines with a circle and an arrow pointing down, a water tap with an arrow pointing down, a gas tap, a water tap with an arrow pointing up, and 4 vertical lines with a circle marked with an arrow pointing up.

Can somebody tell me in terms of left/right/up/down/red tap/black button/any other descriptive detail not involving terms such as "stop tap" which I don't understand, how to repressurise my boiler?

many thanks in advance for anybody who can help.