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How to bleed a radiator

How to bleed a radiator

Does your radiator feel cold at the top and warm at the bottom? It is likely that it needs bleeding. ‘Bleeding radiators’ is when you let out air that has become trapped inside. Trapped air causes the radiators to have cold spots, reducing the efficiency of them. You can bleed your radiators yourself, and it can vastly improve the efficiency of your entire heating system.

Step 1: Turn your heating on

Turn on the heating so that all radiators in your home come on. Remember to wait until your radiators are fully heated before moving on to step two. You need to build up the pressure inside the radiator to be able to force the air out.

Step 2: Find out which radiators need bleeding

Once your radiators are hot, go and check each one individually to see if all parts of the radiator are warming up.  Cool spots, particularly toward the top of the radiator, mean that there could be air or gas trapped and that you’ll need to bleed that radiator. Once you’ve found your cool spots it’s time to move onto step three and bleed them.

Step 3: Bleed the radiators

Switch off your central heating. This is reversing the process identified in step one and will allow you to handle the radiators without burning yourself or soaking your floor.

Bleeding radiators will require a radiator key (buy one at your local hardware store if you can’t find yours) or a flat-blade screwdriver.

At the top of the radiator at one end there will be a valve. You can attach the radiator key to the square bit in the centre or put the end of the screwdriver into the groove.

Hold the key or screwdriver with a cloth, and have another cloth ready to catch any drips, then slowly turn the radiator key or screwdriver anti-clockwise – if gas is escaping you’ll hear a hissing sound.

Once there is no more gas, liquid will come out and the valve will need to be closed quickly. With the more modern screwdriver operated escape valve, liquid is likely to emerge as a jet rather than a dribble.

Step 4: Check the pressure

Check the pressure by having a look at the gauge on your boiler. If the pressure is too low, you’ll need to ‘top up’.  See ‘How to repressurize your combi boiler’.