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How to bleed a radiator

Man Hands On Radiator

Bleeding your radiators is how you get rid of the air pockets that stop hot water circulating around your central heating system efficiently. This in turn puts extra strain on your boiler and costs more money. To walk you through the process, we’ve created this handy guide to bleeding a radiator.

Jump to:

Do my radiators need bleeding?
Before you start bleeding a radiator
Bleeding a radiator step-by-step
What if bleeding the radiators doesn’t fix the problem?
How to bleed radiators without a key
Where to buy radiator keys
How often should you bleed radiators?

Do my radiators need bleeding?

Man Hand Under Radiator

If your radiators are taking longer than usual to heat up, don't seem to be getting as warm as they should, or are making gurgling noises, the likelihood is your heating system needs bleeding.

A good way to check is if your radiators have cold patches at the top but are warm at the bottom. If so, you need to bleed them to let the trapped air escape so that the hot water can circulate freely again.

The good news is that bleeding a radiator is a quick and straightforward task in most cases, and something that most people can do without any assistance from a professional. 

Before you start bleeding a radiator

Turning Off Heating

Before you start bleeding any radiators, you must ensure that the heating is switched off and the radiators are cool to the touch. If the heating is on when you try to bleed a radiator, you run the risk of coming into contact with scalding hot water.

Before you continue, you should also make sure that you have a cloth or jug to catch the small amount of water that may escape when you’re bleeding radiators. You will need a radiator key too. 

Bleeding a radiator step-by-step

Watch the video below to see how you can easily bleed a radiator using a key, and prepare your home for winter. 

1. Find the bleed valve

Locate the radiator bleed valve (where you put the radiator bleed key). This is usually at the top corner of a radiator and looks like a round hole with a square inside. The other top corner of the radiator will usually not have anything on it, so it should be straightforward to find the valve.

Once you’ve found it, place the old cloth or a jug beneath to catch any water that may be released.

Radiator Bleed Valve

2. Open the bleed valve

Insert the radiator key into the bleed valve and slowly turn it anti-clockwise (a quarter of a turn should be enough). You should hear a hissing sound as the air escapes.

Radiator Bleed Valve Open

3. Close the bleed valve

Once the hissing sound stops and water starts to leak out, turn the key clockwise to close the valve. The water will stop leaking out as soon as the valve is closed.

Radiator Bleed Valve Close

4. Check your boiler pressure

Once you’ve finished doing this for each radiator that needs bleeding, you’ll need to check the pressure of your boiler’s water pressure gauge. If the boiler pressure is too low (below 1 bar), you’ll need to repressurise the system.

Boiler Pressure Gauge

5. Check your radiators

If the boiler pressure is now normal (between 1 and 2 bars), you can switch your heating back on and check that your radiators are now heating up as they should.

Woman Hand On Radiator

What if bleeding the radiators doesn’t fix the problem?

If bleeding your radiators doesn’t fix your heating problems, your radiators may need to be drained and flushed. We recommend getting a professional to flush your system.

How to bleed radiators without a key

If you don’t have a radiator key, it is sometimes still possible to bleed a radiator if the valve has a slot in it. Many modern radiators have this design. You can simply use a flat head screwdriver to open the valve and let any trapped air escape from the radiator. Then close it again as soon as the air stops and water starts to leak out. 

Some older radiators can be bled using an Allen key, also known as a hex key, if the bleed valve is hexagonal in shape. 

If neither of these solutions will work for your radiators, you can usually pick up a radiator key that will fit quite quickly, cheaply, and easily. 

Where to buy radiator keys

Most local DIY or hardware stores will sell radiator keys and they are designed to universally fit most common radiators. You can also buy them online. 

If you have a radiator that is very unusual and standard radiator keys don’t fit, you may need to visit a plumbing merchant, where you should be able to pick up a tool that will work. It might be a good idea to take a photo of your radiator bleed valve to take with you to the shop to make sure you get the right solution. 

How often should you bleed radiators?

In order to help prevent issues with your radiators and keep them working efficiently, it’s usually a good idea to bleed them at least once a year. Ideally, this should be done when it starts to get a bit colder, before the heating system is regularly in use again. 

Even if your radiators seem to be working fine and you don’t have any issues, routinely bleeding them every year can help with efficiency and mean that you’re not spending more money on energy costs than you need to. 

Along with bleeding your radiators, there are lots of other things you can do to help get your home ready for autumn and winter.