How to bleed a radiator
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Noticed that one or more of your radiators isn’t as hot as the others? Often nearer the top of the radiator? This could be a sign that your radiator needs bleeding.
Why isn’t my radiator hot?
Problems with radiators occur when small amounts of air enter the central heating system every time fresh water does, for instance when you use water in the house from taps. The trapped air displaces the hot water that normally heats the radiator, and it is this air that needs to released during the bleeding process. Once released, the hot water can flow freely again.
A sign that your radiator needs bleeding
If you have noticed that one or more of your radiators isn’t as hot as the others, often nearer to the top of the radiator, this is usually a sign that the radiator needs bleeding. Small amounts of air enter the central heating system every time fresh water does, i.e. every time you use water in the house from taps etc. The trapped air displaces the hot water that normally heats the radiator and it is this air that needs to be released during the bleeding process. Once the air is released, the hot water can flow freely again.
Most domestic radiators will need bleeding at some point, and it is important for the efficiency of the boiler and heating system that it is done properly. Luckily it is a relatively simple job that can be done by anyone if you follow this guide carefully.
Before you start bleeding a radiator
As air is lighter than water, the air in the central heating system will generally rise to the highest point it can. This means you will probably find that radiators on upper floors will need bleeding before those on lower floors. If you find that those on the ground floor are not heating properly then it might be worth bleeding all of the radiators in the house.
The most important thing you need to do before bleeding a radiator is turn the central heating system off. This is because some water pumps, depending on where in the system they are fitted, can actually suck more air into the radiator and consequently the heating system if they are turned on while you open the bleed valve.
What you need to bleed a radiator
Bleeding a radiator is a relatively simple task. You just need a bleed key, which is also known as a radiator key, and which you can purchase at most DIY shops. An old piece of cloth to catch any drips would also come in helpful! Some modern radiators just require a flat-headed screwdriver instead of a bleed key so check before you buy a radiator key!
How to bleed a radiator
Firstly, turn the central heating off. Then, fit the bleed key or screwdriver into the valve (usually at the top on one end of the radiator, or on the back of the radiator) and turn it in an anti-clockwise direction for about half a turn.
Wrap a piece of old cloth around the key or screwdriver to catch any drips of water that may come out, and be aware that the water can be very hot depending on how recently the system was turned off. Once the valve is open you should hear the hiss of air being released.
Continue to release the air until water begins to drip from the bleed valve and then close the valve by turning it half a turn in a clockwise direction. It is important not to over tighten the valve.
If you have a pressurised sealed system then releasing trapped air may cause the internal pressure to drop and so this should be topped up using the manufacturer’s guidelines.
