There is a plumbing fault with your central heating system that needs to be fixed, to the extent that you have to drain the system. Ashford Plumbers carry this out.Method.1. Turn the boiler off so that the pump is not operating.2. Wait until the water starts to cool.3. Turn off the main stopcock to the supply feeding the expansion tank.4. Go up into the attic and, as a precaution, and just in case the stopcock is faulty or you have turned off the wrong stopcock, Bridge the tank with the batten and tie up the float valve arm so that the water stops running.5. Go down to the drain cock. Slide one end of the hose onto the drain cock outlet and run the other end through the house to the nearest door and out to one or other of the garden drains. Tie the hose securely so that it can’t fall of the drain cock nozzle. (The hose must run level, not uphill).6. With a supply of old cloths around the drain cock, use a spanner or a key to open up the valve.7. Keep a watchful eye on both ends of the hosepipe, especially the end of the drain cock.8. When the water stopped running from the end of the hose, go from one radiator to another slightly opening the bleed valves, so that the last dregs of water run out.9. When you have made your repairs close the drain cock and the radiator bleed valves, remove the stick and string from the tank, and turn on the main stopcock.10. Working from the topmost radiator, bleed each radiator in turn. Finally you must bleed the pump and of course tidy up any mess that you have made. An Ashford Plumber will always clean up.