One of the pointers (the red one, by the sounds of it) is movable by turning the gauge itself or a small wheel in the middle. Leave that on 1 bar, as it is. The other one (usually the black one) tells you the pressure inside the boiler. You need to bring the pressure back up to 1, so both pointers meet. To do this, your boiler has a 'filling loop' - usually a flexible pipe with a tap on one end- and this connects the boiler to the house water main. You need to find this filling loop, and open the tap slowly, watching the pressure gauge rise as you do so, until the pointers meet. (Don't overdo it - or you'll have to bleed water out again). The tap, by the way, may be either hand, screwdriver or small spanner operated. Fill the boiler with the central heating off to get an accurate reading. Hope this helps!
John
January 2008