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    Re-filling central heating system

    Summary: Learn how to re-fill a central heating system.

    There are various problems that may require you to drain your central heating system in order for it to be repaired. And in each case it is important the system is re-filled correctly. The advice given is for an open-vented system; the most common type used today.

    Re-filling a central heating system

    • When all work has finished, you can start the re-filling process. Firstly close the valves on all the bottom floor radiators.
    • To start up the water supply again, you must reverse the way it was switched off in the first place. Either turn on the water to the supply cistern or untie the ball valve; whichever applies.
    • Re-open the valve on one of the bottom floor radiators again and leave it open until water comes flowing out steadily. Close the valve again when the water is flowing and repeat this process with all the other bottom floor radiators. The water supply has been refilled to your system on this floor when all have been completed.
    • Now repeat this same process with all the radiators on all the floors, working your way up from the bottom.
    • Once completed, you now need to see if the water level is high enough in the cistern. This can be established by whether the ball valve is just able to float. If the level of water is too high, release some using the drain valve. Adjust the arm of the ball valve so the valve closes when the water reaches the right level.
    • Replace the lid of the cistern and insulation jacket and use manufacturer’s instructions on how to re-ignite the boiler.
    • When the system heats up, air will be released into your system. This will require you to bleed the radiators to remove it. This bleeding process may have to be repeated over the next couple of days, until the system is in full working order.
    • Finally check the system for leaks. If all is clear then remove the hose from the drain valve, whilst also checking the drain valve isn’t leaking itself. If the valve is not water tight you will have to drain the system again in order to fix it.

    Starting on the ground floor, open one of the radiator air vents and when water comes out in a steady flow, close it.

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