The filling loop will be an external loop between the cold water feed and CH (usually return), there will be two valves (possibly connected by a silver braided hosepipe).
There will be either screw slots or 1/4 turn taps (depending on make of loop), open these slowly, and watch the pressure rise to about 1 bar on the boiler guage (bottom left of the boiler).
Carefree, October 2010
