if it is just a matter of re-filling the tank you need to find the valve on the "main cold water in pipe "which is usually a flat slot-head screw on the cold water pipe coupling.
on my system i have to remove the cover for the pipes which go up to the boiler then turn the screw and you will hear the boiler filling,you'll also notice the pressure guage rising but dont let it rise above 0.5
turn the screw back to stop the water flow when the pressure is ok. be carefull not to damage the screw on the coupling,its brass and easily damaged,,use the correct size screwdriver.hope this helps
KEV
October 2006