turning off the water to my central heatin

[rigger1966]

hi folks
i need to turn off the water to my central heating system as i need to move one of the valves due to having to fit a smaller radiator, i dont want to make a mistake and relize that it maybe a small thing but want to do it right and not cause any other problems any help would be great many thanks
my details of my system are
a glowworm compact electronic with 8 rads on

 

[JPC]

turn the boiler off.
attach hose to drain cock
open drain
wait 17 mins ???
do your changes
fill up and checks for leaks
if ok, drain a bit and add inhibitor.
re-fill to around 1.2 bar