The winter is coming, and it is time to make sure your radiators are in top form for the colder months. But before you start, there are a few things you should know about bleeding radiators. In this article, we will cover everything from how to bleed radiators, what you need to bleed them, how often they should be bled, and any potential problems that could arise.

Radiator Bleed Valve

Why Do Radiators Need Bleeding?

Radiators are bled to remove the air from the central heating system. Air can enter the system in a few different ways, and it will often build up in one or more of your radiators.

Air is compressible and not subject to boiling so having air in the system can make radiators inefficient and you will often notice that a radiator containing air will heat up at the bottom and stay cold towards the top.

How Often Should Radiators Be Bled?

Although each system is different, in general terms, we recommend that radiators should be bled a minimum of once per year, even if they appear to be working just fine.

The frequency your radiators may need to be bled can also depend on how much they are used, where they are located in your home and the type of system that you have.

For example, the radiator at the highest elevation in your home is the one that is likely to collect any excess air in the system and will often need bleeding far more often than a radiator that is downstairs on the ground floor. This is because hot air rises.

What You Need to Bleed Radiators

You will need a couple of items before you can bleed your radiators. Make sure that you have the following:

Radiator Bleed Key

A radiator bleed key is like a small wrench with an offset head. The purpose of this tool is to be able to open up the bleed valve present on each of your radiators.

Towel or Cloth

You will need a towel or a cloth when bleeding your radiators, this is to catch the excess water that will escape when bleeding.

Stelrad Radiator Bleed Valve
Old Stelrad Radiator Bleed Valve

How to Bleed a Radiator

Once you have your radiator key and cloth, you are ready to begin bleeding your radiators. This is a simple task that anyone can do so you do not need to worry about calling out anyone to help.

Step 1 – Turn off the System

The first step is to ensure that the system is turned off and if the system is on a timer, you will need to be sure that it will not be coming on whilst you are bleeding your radiators.

This is purely for safety reasons as it is extremely unwise to attempt bleeding a system whilst it is hot. It may not only be too hot to touch but when you are bleeding each radiator, there will be small amounts of water escaping so you need the system off to prevent scalding!

Step 2 – Safety First

Before diving into the process of bleeding your radiators, safety should always be your primary concern. This simple yet essential task, if done without due care, can result in injuries or damages.

Here are some guidelines to ensure safe and effective radiator bleeding:

  • Protective Wear: Always wear gloves to protect your hands from potential scalds or cuts. While the water that comes out should only be lukewarm, there’s always a risk, especially if the system was recently turned off.
  • Eye Protection: Use protective eyewear. Though it may seem excessive, it’s always better to be safe. A sudden spurt of water mixed with rust or debris from the radiator can inadvertently get into your eyes.
  • Prepare Your Work Area: Place towels or absorbent cloths around the radiator. This not only prevents water spillage on your floor but also gives a clear indication of any leaks that may occur.
  • Check the System’s Temperature: Ensure the heating system has cooled down. Bleeding a hot radiator increases the risk of scalding. Always make sure the system has been off for a sufficient amount of time, and it’s cool to the touch.
  • Avoid Force: If a bleed valve is stuck or doesn’t turn easily, never force it. Using excessive force can damage the valve or radiator. Instead, try gently tapping it, as mentioned later in this guide. If it still doesn’t budge, it might be time to consult a professional.
  • Children and Pets: Ensure that children and pets are kept away from the area while you’re working on the radiators. Not only can they be at risk from the hot water, but they can also pose a distraction, increasing the chances of mistakes.

Step 3 – Work out Your Order

Whilst your system is cooling down, work out in which order you are going to bleed your radiators. Although this is not the most important step, being a little more organised will help some people.

You will want to plan your route to start at the furthest, lowest point in the system and then work through each radiator until you get to the radiator at the highest elevation in your home.

Step 4 – Bleeding the Radiators

  1. Locate the bleed valve at the top of your radiator, usually at one end but they can be hidden in the back of some.
  2. Hold your cloth underneath the valve in preparation to catch any water that will escape and using your radiator key, slowly turn the valve anticlockwise until you either hear a gentle hissing sound or see water escaping.
  3. If you see water escaping immediately, close the valve and move on to the next radiator.
  4. When you hear the gentle hissing, that is the air escaping so hold the valve key in place until the hissing stops, and you get water escaping instead.
  5. Again, once the water begins to escape, close the valve, and move on to the next radiator.
Radiator Bleed Key
Radiator Bleed Key

Step 5 – Repeat

Repeat step 3 for all of the radiators in your house starting from the lowest elevation right through to the radiator at the highest.

Step 6 – Re-pressurise the Boiler

One step that many people unintentionally skip is to re-pressurise the boiler after bleeding. Check the pressure gauge and if it is too low, it will need re-pressurising. When cold, the pressure on the gauge should show just over 1 bar.

Although there are a lot of different boilers, they will all usually have a lever or tap that can be turned to increase the pressure – this is known as the filling loop.

Step 7 – Turn Your Heating System Back On

The next thing to do is to turn your heating system back on to ensure that all of your radiators are heating up evenly and that there are no cold spots remaining.

If there is still a cold spot or a particular radiator not heating up properly, repeat the process again – if following the second time of bleeding, you are still having cold spots, this could indicate a more serious problem such as a blockage somewhere.

Problems That Could Arise When Bleeding Radiators

There are several problems that could arise and to save you from standing there scratching your head, we have covered some of the more common ones below to try and help you get your system sorted without professional help.

No Bleed Valve on Radiator

It is a common occurrence that many people are unable to locate the bleed valve on a radiator leading them to believe that in fact there is no bleed valve on a radiator.

If you think that there is no bleed valve on your radiator, you have made a mistake and have just been unable to locate it. Some bleed valves are located on the back of radiators under small covers or caps, and I have also come across some towel rails that have the bleed valve extremely well hidden.

If you think there is no bleed valve on your radiator, have another look, it will be there.

Radiator Key Doesn’t Fit

This is another common problem that people come across when they finally get around to bleeding their system – the radiator key doesn’t fit. This could be down to the age of the radiators or simply the design.

Although many bleed valves will be the same from different manufacturers, there are some out there that like to keep us on our toes.

In this case, if you have a radiator where the key doesn’t fit, you are likely to need to find one that does. Any good plumbers’ merchant should have a replacement for the valve you are trying to access.

No Water in the Radiator When Bleeding

You may have come across a radiator that appears to have no water in it. You may have heard the hissing sound and then it has stopped, and no water has tried to escape.

Having no water in a radiator when bleeding is almost always down to the pressure in the system.

What to do if no Water Comes out When Bleeding a Radiator?

If the hissing sound has stopped and there is no water coming out, this means that the system lacks the pressure to push the water high enough to remove the trapped air.

We recommend re-pressurising your boiler using the filling loop to ensure that the pressure is sufficient enough to let the air escape when bleeding.

Signs That You May Need a Plumber

Occasionally, you may come across another issue that you cannot resolve and being able to identify the signs that professional help is needed can save time, avoid further complications, and ensure a warm home.

Here are several signs and symptoms indicating it might be time to call in a plumber.

Persistently Cold Radiators

If after bleeding your radiators they remain cold or only partially warm up, there may be a more serious underlying issue such as a system blockage or pump failure.

Excessive Noise from Boiler or Radiators

Continuous noise like banging, whistling, or gurgling from your boiler or radiators can indicate a more serious issue. While some noise like a gentle whirring is normal, louder, more abrupt noises should be investigated by a professional.

Frequent Need for Bleeding

If you find yourself needing to bleed your radiators frequently, this may signal an ongoing issue with your system. A well-functioning system should only need bleeding once or twice a year at most.

Discoloured or Murky Water

If while bleeding your radiators you notice the water is discoloured or murky, this could indicate corrosion within your system which may require a system flush or other professional services.

Inconsistent Heating Across Radiators

If some radiators are hot while others are cold, there might be an imbalance in your system that requires professional adjustment.

Low System Pressure

If the pressure in your system remains low even after bleeding and re-pressurising, a professional should be called to identify and fix the issue.


Any visible leaks around your radiators, pipes, or boiler should be inspected by a professional to prevent further damage.

Unable to Locate or Access the Bleed Valve

If you are unable to locate the bleed valve, or if it’s stuck and you’re unable to open it without applying excessive force, it’s safer to call in a professional.

Boiler Fails to Re-ignite

If after bleeding your radiators, your boiler fails to re-ignite, this could indicate a more serious issue requiring professional assistance.


Bleeding your radiators is a regular maintenance task that needs to be done on a yearly basis and is one of the most important things you can do besides ensuring your system is functioning efficiently and cleanly.

When we bleed our radiators, we are removing trapped air which causes cold spots in specific areas or can make some radiators heat up at the bottom only or not heat up at all.

How to Bleed Radiators Infographic

Plumbing Wizard Tips

“Ensure you have a cloth, towel or rag handy to catch any escaping water – you don’t want to have wet carpets!”

“Ensure the heating is turned off before bleeding the system – heating systems are HOT, and scalding does occur!”

“Remember to check the boiler pressure after bleeding and ensure that it is at or just above 1 bar!”

“If your radiator key doesn’t fit, do not panic, your local plumber’s merchant should have one for you!”

Frequently Asked Questions

Which radiators do you bleed first?

You should start at the furthest, lowest point in the heating system and bleed your radiators in order of elevation finishing with the highest.

How do I know if my radiator needs bleeding?

There are various ways to know when a radiator needs bleeding. A radiator may heat up slowly, it may heat up at the bottom only or it may not heat up at all.

You may also hear gurgling, creaking noises from the radiators as the water is forcing its way past the trapped air.

If you practice good maintenance of your radiator system, you should bleed them annually regardless of whether they appear okay or not.

Should water come out when you bleed a radiator?

Yes, when you are bleeding your radiators, you should expect a little water to escape. It is the water pressure inside the system that is forcing the air up and out – as soon as you get water emerging from the bleed valve – turn it off!

If the air stops hissing and you are yet to see water, it is likely that the boiler needs repressurising.

Can I bleed a radiator without a key?

Yes, you can bleed a radiator without a key although it may be a little more fiddly. You are best to try needlenose pliers to bleed a radiator if you do not have a key, but depending on the bleed valve, you may be able to try other tools such as a flathead screwdriver.

What does it mean when my radiator is cold at the top?

A cold radiator at the top may indicate that it needs to be bled to remove excess air.

How often should I bleed my radiators?

It’s generally recommended to bleed your radiators once a year, or as needed if they are not heating up properly.

What do I do if the bleed valve is stuck?

If the bleed valve is stuck, try gently tapping it with a hammer to loosen it. If it still won’t budge, you may need to shut off the water and replace the bleed valve.

Can bleeding a radiator fix low pressure in my heating system?

Bleeding a radiator can help with low pressure if the problem is caused by air in the system, but it may not be the only solution.

Can bleeding a radiator cause damage to the system?

If done properly, bleeding a radiator should not cause any damage to the system. However, it is important to make sure not to over-tighten the bleed valve or let it leak.

What should I do if I have a lot of rust coming out of my radiator when bleeding it?

If you see a lot of rust coming out of the valve when you are bleeding, it would indicate corrosion somewhere in the system. Your system may need flushing or in worst-case scenarios, the radiator may need replacing.


Lee Pearce is not just a master plumber; he’s a veritable Plumbing Wizard. With over 30 years of experience in the trenches of pipes and drains, Lee has become the go-to sage for DIY plumbing, saving homeowners thousands in potential call-out charges. As the founder of Plumbing Wizard, he’s dedicated to demystifying the complexities of home plumbing, offering easy-to-follow advice that stands the test of time and pressure. His online blog is a treasure trove of tips, tricks, and tutorials that empower everyday individuals to take charge of their home’s plumbing health. Lee’s practical wisdom is not just about fixing leaks; it’s about imparting confidence and self-reliance. When he’s not writing or elbow-deep in a plumbing project, Lee is passionate about educating the next generation of DIYers, ensuring that practical skills are passed down and preserved.

More You Might Like