No pressure in PowerMax boiler

Hello, we've moved into an apartment which has a Powermax 155 Boiler in it. Everything was working fine for us until this Sunday when the boiler just stopped working, thus resulting in no heating and no hot water. We've had a look and the pressure dial is at zero. Would you know why we have lost pressure in the boiler and how we can fix this? Is this something we can do, someone here at work mentioned venting the boiler? Or should we get a plumber out to take a look? The boiler was last serviced on 22nd Sept 2005.

Thanks in advance (and hopefully I included all relevant details!)

Could be any one of a few problems but start with filling the system up again to its regular pressure (1.0 to 1.5 bar) run the system. First check the pressure relief outlet (15mm copper pipe coming out of the wall running down to approx 6-8 inches off the ground) is not showing any signs of weeping. If thats ok go round the house and check all radiator valves. If no signs of any water loss you really do need proffesional help! You may get baffled by all the technical jargon. If you feel you'll understand then post back and I or any one of my learned colleagues will try to talk you through it.