I have a greenstar cdi central heating boiler, a pipe run to one of the rads has to be moved(but not the boiler or rad), how do you drain the system to allow re-run of pipes and bleed the rad?[color=blue][/color][size=18][/size]
First find the drain valves they might be outside or below a radiator (they should always be the lowest point in the system)
Once you've found the drain valves turn off the boiler and open them - use a air key to let air into the rads (starting upstairs working down)
When no more water comes out from the drain valves you can cut into and move your heating pipes (keep a cloth and small bucket handy for residual water)
Oops, forgot to mention turning off the water in my earlier reply.
The safest option would be turning off the main stopcock for a few hours till the work's complete but if this isn't an option you could do whichever one of the following applies to you:
If you have a combi, just make sure it's switched off and you shouldn't need to worry about turning anything off, though you'll need to connect the filling loop underneath the boiler to re fill but if you have a systems boiler (seperate hot water tank) you'll probably have a small feed and expansion cistern in your loft to feed your primary hot water (central heating water). You will need to turn this off before you start to drain down the system.