Right.
Look at the pipework coming out below the boiler.
Linking two of the copper pipes there will be a length of silver flexible hosepipe (a bit like shower hose). This makes a "bridge"; one end of the flexible pipe is connected to the cold mains (usually the narrower copper pipe) and one end connected to the heating return pipe (this is the thicker copper pipe).
At each end of the flexible hose there will be a valve. They may look like black levers, or little taps, or you may have to turn them with a screwdriver (like a service valve you might see under a tap - the slot in the screw will be in line with the pipe when the valve is open, and across the pipe when it's closed).
Open the valve on the heating end of the flexible pipe first.
Next open the valve on the cold mains end SLOOOOWLY, don't open it all at once. You will hear water rushing through the hose if you've got it right.
Watch the pressure gauge on the boiler.
When it gets to about 1.5 bar turn the valve off, then turn off the other one.
Job's a good 'un.
If you can't see the flexible pipe anywhere (and plumbers have been known to put them in weird places) it may be that yours has been removed and capped off, which is strictly speaking quite correct. Look for the connection points on the pipes below the boiler and then have a grub around for the hose (it's called a filling link). Try on top of the boiler, it sometimes gets stashed there for safekeeping.
Bunslinger, June 2009
