How do I drain down my central heating system with no drain valve?

Fit a self cutting tap like this- <a href="http://www.ultimatehandyman.co.uk/how_to_fit_a_self_cutting_tap.htm" rel="nofollow">http://www.ultimatehandyman.co.uk/how_to...</a> to one of the pipes downstairs that feeds a radiator, then drain off all of the water, you can then fit a drain off valve.  more

You turn off the mains water feeding your system (usually its the one feeding your big tank)then go to your last rad close the valve at the start of it then open the valve at the end and drain that rad,once that rad has drained fully disconnect the end of the rad and connect a hose to the rad and run the hose outside .Turn the valve on on all the rads and allow the system to drain.  more

It is very strange or careless not to fit a drainage valve to the system. Turn off the mains tap. If it is a house with more than one floor, you can drain it by opening the air-bleeder tap on top of the radiator that is on the lowest level of the building. Gravity will force the water out if you also open the air-bleeder tap on the top floors (wait till the level is down or water will also gush out from it too). There will still be water left in the radiators on the ground floor and if you want to drain it completely, you will have to get a pump and insert a small tube down the air vent to suck it out. All this will take time, and I would take the opportunity to change one/two of the valves for one with a drain.  more