look for the flexi silver braided pipe under the boiler thats the filling loop.
open the valve on that and watch the gauge you can hearthe water going in.
fill to about 1.5 bar.
you'll have to bleed the rads as the pressure has gone so low.
bleed one at a time but keep checking gauge and keep filled to 1.5 bar.
hi-spec plumbing, August 2007