Drain Your System

If you have a vented system fitted, there should be something called a feed and expansion tank that will allow for the varying water levels in the system as the water heats up and cools down. The tank also lets the water top up as needed by the use of a float valve. Bankside Plumbers can drain any system. To begin the process, follow the guide below:
Isolate the boiler from its power supply, and let the water cool down. This will stop you getting scalded.
Isolate the water for the system by shutting the inlet valve on the inlet fitted on the feed and expansion.
Find the system drain point. Normally at the lowest point of the system it should be on the pipework near to the lowest radiator. Connect a length of rubber hose to valve with a jubilee clip. Just in case, put a bowl under the connection in case there is a slight leak, and now take the other end of the hose to a suitable outside drain.
Make sure that the valves are opened up on all the radiators. This is so that all pipework will be drained. South Bank Plumbers carry the tools for the job.
Next, open up the drain valve by slowly unscrewing the square head with a spanner or small wrench, holding the body of the valve with a wrench to stop it turning.
Visually check the water is draining outside.  
Now, open the vent (air) on the top of the upstairs radiators, this will let air in to replace the water.
When the system water level drops under the height of the downstairs radiators, you can now do the same thing for the lower radiators.
When the water has stopped, the system is now empty. Now you can do repairs or servicing