you have to conections generally beneath the boiler one is the cold mains feed to boiler known as a filling loop. with this loop normally has a silver flexible hose. this should always be removed once filling the boiler. because of contamination, from heating to cold mains water. generally they are fitted with one isolation valve & double check valve.
simply join the 2 ends one to the cold mains feed to boiler & the other to CH F or CH R which ever has the filling loop conncted to it.
slowly open cold feed on loop & then open the other end connected to CH F/R until the pressure readiong on gauge reads 1 - 1 1/2 bar then isolalate mains cold feed then the other valve on the loop.
make sure that you vent your radiators to let out excess air.
if system falls below 1 bar then repeat loop process til at correct pressure. look for manufacturers sytem pressure.
make sure that the loop conections are removed once filled.
get a conmpetent person to do the job.
gary, April 2009