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How to bleed your radiators to improve energy efficiency

When you bleed a radiator, you release air that has become trapped inside, which improves the efficiency of your heating system. This means a warmer home and cheaper energy bills. You can do it yourself — we'll explain how.
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Step 1: Turn your heating on

Turn on the heating so that all radiators in your home are operating.

Remember to wait until your radiators are fully heated before moving on to Step 2. You need to build up the pressure inside the radiator both to work out whether there's any air trapped inside and then to force the air out.

Step 2: Test to find out which radiator(s) need bleeding

Once your radiators are hot, check each one individually to ascertain whether 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 inside it, which will need to be let out in order for the radiator to properly function.

Once you've found your cool spots, it's time to move on to Step 3 and bleed the affected radiators.

Step 3: Bleed the radiator

Now that you've identified which radiators need bleeding, you can switch off your central heating. This will allow you to handle the radiators without burning yourself or soaking your floor.

Bleeding radiators will require a radiator key (which are readily available at most local hardware stores if you don't have one) 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, water will come out and the valve will need to be closed quickly. With the more modern screwdriver-operated escape valve, the water is likely to emerge as a jet rather than a dribble, so stand clear!

Step 4: Check the pressure

Because water will inevitably exit the system when you bleed the radiator, this will reduce the pressure of the system as a whole, which can limit its effectiveness. There should be a gauge on your boiler to allow you to check the overall pressure of the system. If it's too low, you'll need to top it up by using the lever or tap on your boiler, known as the filling loop.

The exact process may differ from boiler to boiler but basically involves allowing cold mains water into the system until the pressure returns to an optimal level. Check with your boiler manufacturer if you're unsure, as most (if not all) of them will have tutorials on their websites for you to follow.

Afterwards, you may want to run another test to check that your efforts have been successful. Simply turn your heating on, wait for all the radiators to heat up and check for any cool spots.

What are automatic radiator valves?

Depending on what type of radiator you have, it may be possible to automate the process of bleeding your radiators by using an auto vent.

Auto vents are automatic radiator bleeders that attach to your valves, which means you'll need one per radiator. The vent lets out air gradually, increasing the effectiveness of your radiator and meaning your boiler doesn't have to work so hard.

How else can you improve your heating?

There are plenty of other gadgets that are designed to improve the effectiveness of your heating.

Radiator insulation foil, for example, is a simple way of ensuring your radiators heat your room, as opposed to your walls. It sits behind your radiator and reflects the heat that is generated back into the room. It's widely available in hardware shops and you should be able to install it yourself.

A slightly more expensive option is the radiator booster. This is essentially a stretched fan unit that sits on top of your radiator and pushes the warm air generated around your room. While the radiator booster will use electricity to run, they will save you more on your heating bills.

If you've ever wondered whether it's cheaper to heat the whole house or just the rooms you're using, you'll find the answer in our guide.

It's also important to ensure the heat being generated isn't being wasted by keeping your home and rooms well insulated. Draughts around window and door frames are at the easier end of the spectrum, but you can take on more significant and expensive insulation measures, such as refreshing wall and attic insulation. This costs more up front but will save you more in the long-term.

To learn more and to see whether your home is suitable you can read our guides to loft insulation and wall insulation (and more) in our insulation guide section.

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