Draining a fully pumped heating system makes it easier to work on the system. To exchange metal radiator valves or add an additional radiator as an example. This is often implemented by the engineer during repair or extension work although some experienced officeowners have been known to drain their own gas central heating systems.
The main reason for most people for Emptying their water tube boilers is to clean the radiators. Before you do anything to the actual metal radiator you should switch off the gas boiler and any gas or electric that supplies the central heating boiler. Another essential step is to ensure that no additional water enters the gas central heating system whilst you are Flushing it.
Your Central Heating tank is where the water is fed into the system. The expansion cystern uses a ball-valve similar to that in a toilet system. As the water level rises the ball floats on the surface and closes off the valve. Water is added to the heating system if the levels fall as the ball will drop on the water surface opening the valve. To ensure that the gas heating system fully empties we need to stop this mechanism. To prevent any more water entering the valve needs to be off.
Now take a hosepipe emptying into an outdoors empty and attach this to the outlet valve on the bottom of your metal radiator. Water will now flow out of the metal radiator through the hosepipe into the external empty. As there will be water in the bottom floor radiators you will need to attach the hose to one of these to see to it that the whole central heating system drains. You must make sure before you start cleaning or replacing your heating radiator …