How to refill a central heating system efficiently

If you're treating corrosion or replacing or moving a radiator, then a very useful skill is to know how to drain and refill your central heating system.

Drain out the water

The first thing to do is to drain all the water out of your system. In order to do this, you'll need to switch off your central heating system and locate and turn off your mains water supply, which will stop the system from refilling with water.

Take a piece of hosepipe and attach it to the drain-off valve on one of your downstairs radiators. The hosepipe will need to be long enough to go outside, into a bath or into a bowl so that the old dirty water can be collected and discarded.

Using a spanner, unscrew the bleed valve and the water will start to flow out. You can leave this process to it's own devices for 10 - 15 minutes to ensure that all the water has flowed out.

If you wanted to flush out a radiator, you can do it at this point by removing the rad from the wall, taking it outside and flushing it through with water. This is a useful thing to do if you know that radiator sludge has settled at the bottom of your rads.

Close all bleed & drain valves

At this point, you will be ready to refill your central heating system. Go round each radiator and close every bleed valve and drain valve and, if you have a feed and expansion tank, release the ball valve. You can then switch the mains water supply back on.

After a short while, your central heating system will start to refill with water. At this stage, it's also a good idea to add some chemical inhibitor into your system to slow down the rate of internal corrosion.

Bleed out the air from your rads

It's important that you now bleed your radiators to ensure that any air trapped in the system can escape. Take your radiator bleed key and start by bleeding the air out of radiators on the ground floor and work your way up the house. Have a towel or cloth with you to avoid any spillages onto the floor.

To be really thorough and ensure maximum efficiency, you can repeat the air bleeding process twice just to be certain that there's no air left in the system.

Switch on the boiler & check for leaks

Once your central heating system has refilled fully, you can switch your boiler back on and check that all is working smoothly and your radiators are getting hot.

Take the time to go around each radiator to check all valves are tightened and that there's no leaks.


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5 July 2019