central heating system

Turn off the gas or electricity supply to the boiler .

In your loft you will have a tank called a feed and expansion tank. Its recognizable by a pipe coming in at the top which is the expansion part of the equation. If the water gets too hot in your system the steam can expand, via the pipe, into this tank.

To make sure no water comes in while you are draining the systemyou should put a piece of timber across the tank, lift up the valve arm and tie it to the timber. This will close the valve.

Now connect a hosepipe to the drain nozzle (which is normally on the radiator nearest to your front or back door) run it outside to lawn or drain. Open up the drain valve and let the system run through.

The water will run faster if you open any bleed valves on the radiators starting with the radiators upstairs. As the water level drops you can open the bleed valves downstairs radiators to.

When no more water comes out make sure that the system is finished before you remove radiators or start work. There is a chance that some air has got into the system and locked the water from escaping. Go into the loft and fill the tank with about 150mm of water by loosening the arm you tied earlier. This should start running out of the hose. If it doesn`t you have an air lock and should connect the hose to the cold tap and send a short blast of water back into the radiator you are draining . Make absolutely sure the hose is well attached to the radiator drain nozzle.

Filling the system

Close the drain cock on the radiator and all the bleed valves that you have opened. Untie the string & let the water fill up the system through the tank. Wait until the tank stops filling and go downstairs to bleed the radiators. When they have been bled repeat with the upstairs. This should make sure your system is filled.

Fully open any radiator valves, including heated towel rails, and run your central heating for ten minutes. Turn off the system. Put the radiator key into the valve in one of the top corners of the first radiator and slowly turn anti-clockwise. Have a cloth handy to catch any drips.If air is trapped in the radiator, it will escape through the valve and there will be a hissing & bubbles coming from the valve as the air comes out. As soon as water begins to run freely, close the valve again and wipe away any water.
repeat this for each radiator. Take care not to open the valves more than necessary. Often air pockets will only occur in one or two of the radiators,mainly upstairs. Turn the heating on and check there are no dripping valves. Tighten if necessary.

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