...anyway, an outside tap is used in the video...I suppose that might be necessary if you have to cut off the water supply within the building....in order to work on the radiators....and this building doesn't appear to have an outside tap...presumably why no other plumber has bothered to suggest 'powerflushing' before....go figure....

http://wiki.diyfaq.org.uk/index.php?title=Central_heating_flushing