How to bleed a radiator – how to keep your heating working efficiently

Keep your house warm and your energy bills down this winter with our simple guide on bleeding a radiator

room with radiator
(Image credit: Future PLC)

Summer is over, folks. And now that the weather has turned, more and more people are taking the opportunity to turn on their heating. But if you don’t want to deal with a hefty plumbing bill, it’s probably a good idea to learn how to bleed a radiator. 

Experts agree that there’s a perfect time to turn on the heating, and it's likely earlier than you think if you don't want to run into issues with your heating when you most need it. They also agree that you need to maintain and care for every aspect of your central heating system - from the boiler all the way down to the radiators. 

It’s good practice to bleed your radiators once a year. This task won’t just keep your tootsies warm; it’ll also help you save energy. 'Keeping your radiators well-maintained will save energy as they’ll function more efficiently,' explains Greg Richardson, Head of Marketing, Toolstation. 'If your radiator is cold at the top but hot at the bottom, it means there's air in the system and it needs bleeding.'

Learning how to bleed a radiator is an easy job, however, if you're still experiencing issues afterwards, it might be worth looking into how to flush a radiator, so you can make sure you're getting the most from your central heating this winter.

Grey panelled radiator against white wall in living room

(Image credit: The Radiator Centre)

Why should you bleed your radiators?

'Radiators with trapped air in can be a big problem, as it means that your heating system will have to work harder than it needs to in order to reach the desired temperature,' explains Parv Sanegra, Managing Director, City Plumbing. 'This will mean that you are using excess energy, and spending money you don’t need to.'

Aside from heating efficiency, leaving trapped air inside your radiators could go on to cause problems with your boiler further down the line. 

'Failing to bleed a radiator can cause internal corrosion and damage parts linked to the boiler', says Jessica Steele, Heating Technology Specialist, BestHeating. 'So it's important to bleed radiators around the home yearly.'

room with wooden flooring radiators

(Image credit: Future PLC/Lizzie Orme)

How to bleed a radiator 

Fortunately, learning how to bleed a radiator is simple, and you can do the job in 10 minutes. Before you start, check you have a bleed key that fits your valve (this should be located at the top of your radiator). 

Some modern radiator valves can be opened with a flat-headed screwdriver, but if not, you can buy a valve key from Amazon for £3 and most DIY stores. You'll also need a cloth and bowl to catch any drips.

1. Identify the radiators that need bleeding

Tall white radiator on dark grey wall in living room

(Image credit: BestHeating)

To check which radiators need bleeding, turn your heating on and let your radiators heat up. Then check them for cold spots by running your hands along the top of them. Any that are hot at the bottom, but cooler at the top, probably have trapped air inside them and need bleeding. 

However, it’s important to note that if your radiators are completely cold you may have a bigger issue at hand. It may be that you have a problem with your boiler, you have a leak in a valve, or you have a build-up of sludge at the bottom of your radiator.

But if your radiator still feels hot at the bottom, you’re safe to continue to the next step.

2. Turn your heating off

Once you know which radiators need bleeding, turn your central heating off and allow your radiators to cool down. This is important, or you risk covering the floor with water and scalding yourself.

While this step will take up more of your time, it’s important that you turn off your central heating before opening up any valves for your own safety and for the safety of your home. 

3. Protect floors and walls

Bleeding a radiator can be a fairly messy business, especially if you have a stiff valve that requires some extra force to close. Because of this, it’s always a good idea to protect the area around you before you get started. 

The easiest way to do this is to lie a towel on the floor to prevent any spillages. Then, wedge another behind the radiator to protect your wall from getting wet, too.

4. Locate the valve

Orange radiator with silver valve on black and white floor

(Image credit: BestHeating)

The radiator bleed valve is a small metal square or screw found inside the surrounding nut. It will be located on one side of the radiator, often towards the top.

5. Open the valve

Next, put the bleed key into the valve. You should feel them lock together. Have your cloth ready to shield your hand and a small bowl to catch any small drops of water. 

Slowly turn the key anti-clockwise about a quarter turn. You will hear a hissing or gurgling sound as any trapped air escapes. 'Never open the valve fully because once you bleed air from the radiator water will come rushing out', says Christian Engelke, Technical Director, Viessmann

Continue to hold the radiator bleed key until the air stops coming out. When the first trickle of water appears, close the valve by turning the key clockwise.

6. Finish up

White radiator in front of blue wall next to console unit

(Image credit: BestHeating)

When you close the valve, ensure it is nice and secure without overtightening it. Remove the key and wipe away any water that’s escaped to stop the radiator rusting.

7. Repeat and reheat

Repeat this process on any other radiators in the house that need bleeding. It should only take around 20 to 30 seconds to bleed a single radiator.

'Once you have completed the task of bleeding all your radiators, you may need to re-pressurise your heating system', says Christian from Viessmann. 'If the needle gauge on your boiler has dropped from green to yellow, you'll need to locate the central filling loop connected to your boiler, which looks like a tap. Turn the tap to slowly readjust the pressure.'

Once your boiler's pressure is back up, turn the heating on. The cold spots in your radiators should have disappeared.


Can you bleed a radiator when the heating is on?

'When bleeding a radiator, the first step is always to turn off your central heating and allow your radiators to cool down,' says Greg Richardson, Toolstation. 

It's very important to turn off your heating before you begin bleeding a radiator, to minimise the risk of burning yourself. The radiators fill with hot water when the heating is on, and as some water usually escapes during the bleeding process, it's essential that this is at a cool temperature. 

'Be patient and allow the radiators to cool down before you begin, as the last thing you want is to have hot water burn you when trying to bleed the radiators', says Jessica, BestHeating. 

How do I know if my radiator needs bleeding?

Aside from checking all of your radiators for cold spots when your heating is on, there are some things to look out for which may signify that your radiator needs bleeding. 

'If you can hear gurgling sounds when your heating comes on, or if the radiator takes a long time to heat up, then it is likely there is trapped air', explains Christian. 'This is preventing the hot water from filling the radiator fully.'

The biggest tell-tale sign that your radiator needs bleeding is if it is colder towards the top, and hotter towards the bottom. Carefully running your hands along the top of your radiators once your heating has kicked in will allow you to easily identify which ones need bleeding.

Do you drain all the water when bleeding a radiator?

Unlike flushing a radiator, the aim when bleeding one is to let the air escape rather than the water. It's inevitable that some water will leak out of the valve when you open it, but you should close this again when all the air has escaped and only water is coming out. 

'When only water is dripping from your radiator, then you have completed the bleeding process,' explains Christian. 'That's when you should turn the bleed valve key clockwise to seal the radiator back up.'

You want to avoid letting a lot of water out of the radiator as this will decrease the pressure in your boiler tank. 'If a large amount of water escapes then your system may have difficulty heating the top floors of your property or the central heating system can fail entirely,' Christian warns.

Which radiators need bleeding?

If your radiators are cooler in one area of the house, the radiators aren't properly balanced. The nearest radiators to the boiler are taking more than their share of the hot water from the system. If you have bled one that you know is blocked, check the rest of your radiators.

Often trapped air will only occur in one or two. When you're happy that you've removed air from any faulty radiators, turn the heating on and check there are no drips. Make sure the problem has been irradiated.

living room with pink sofa

(Image credit: Future PLC/Jody Stewart)

How often do you need to bleed your radiator?

It is best practice to bleed radiators at least once a year to release any trapped air in the system. This simple task will ensure your radiators are working more efficiently, preventing any problems occurring with your boiler – caused by air pockets.

And while you can do this at any point of the year, it’s suggested that you bleed a radiator just before you plan on turning the heating on for winter. 

Brett Cullen, Head of Content and Brand at Plumbworld, says, ‘It’s important to bleed your radiators once a year when it starts to get cold, usually during the autumn. Bleeding your radiators will ensure they warm up fully, work efficiently and reduce the strain on your boiler. Bleeding a radiator can help to prevent other issues with your heating system and boiler, making it a fantastic cost-saving solution.’


Tamara was Ideal Home's Digital Editor before joining the Woman & Home team in 2022. She has spent the last 15 years working with the style teams at Country Homes & Interiors and Ideal Home, both now at Future PLC. It’s with these award wining interiors teams that she's honed her skills and passion for shopping, styling and writing. Tamara is always ahead of the curve when it comes to interiors trends – and is great at seeking out designer dupes on the high street. 

With contributions from