How to Bleed a Radiator? A Step-by-Step Guide

Understanding how to bleed a radiator and when to do it is vital for helping keep you home feeling warm. It can help save you money on your bills while also helping you do your bit for the environment – more on this in a bit.

After all, your radiators are just as important as your boiler, so if you are paying energy bills to heat up an inefficient system, then you are not getting your money’s worth of heat. Understanding how to bleed a radiator is key to ensuring their health and longevity.

What does bleeding radiators mean for homeowners?

First, its’ important to understand what bleeding radiators means. Bleeding radiators is the act of removing unwanted air from the heating system. Hopefully your heating system has the right chemicals in it to ensure that the inside of the system doesn’t suffer from rust – which is a black magnetite sludge in your heating system that can settle in awkward parts of your radiators and impede water circulation around the system. Air is another natural element that, when trapped inside the system, can contribute to a rusting system, and consequently lead to leaks and other issues.

Remember, air + water + metal = RUST!

Therefore, it’s in your best interest as a home owner to ensure you are bleeding radiators properly and regularly enough, especially if you’ve invested in designer radiators.

When & How to Bleed a Radiator UK

Part of understanding how to bleed a radiator is understanding when to do it. A few questions to ask yourself when assessing your radiators are:

  • Does the top section of your Stelrad Radiator feel cool to touch, while the bottom of it is nice and warm?
  • Does the entire radiator feel cold?
  • Do you hear gurgling noises as your Heating system is running?

If you’ve answered yes to any of the above and notice cold spots in your radiator, it often indicates that air is trapped inside the radiator which has risen to the top. Therefore, you need to release (or bleed) the air trapped in your radiator, so the radiators can heat effectively when in use. No need to worry though as this is a very common problem which you can easily fix with a few simple tips.

Part of knowing how to bleed a radiator UK involved understanding how often it needs to be done. At Stelrad, we recommend bleeding radiators in the home needs to be done a minimum of at least once a year – each one in the home. You may be surprised how much air you can get out of radiators that seem OK.

Bleeding a Radiator UK – When to Speak with Professionals

When bleeding a radiator UK, there may be times when you notice there are numerous cold or lukewarm radiators in your house. If this is the case, then unfortunately it could mean there’s a larger issue with your home heating system. Fear not, as we have a friendly team here to help should you need some advice. You can also contact a local plumber to see if your boiler is malfunctioning or to see if you need to flush your heating system completely.

Another sign of an inefficient home heating system is when the radiators on the ground floor are hot but other floors are cold. This can suggest circulation issues (pump) in your home heating which might be struggling to move the hot water through the system. If you notice this while bleeding radiators, then we recommend calling a professional to check your full system.

Bleeding Radiators – A Step by Step Guide

After diagnosing the issue with your radiator, follow these simple steps to bleeding radiators in your home. Please refer to the photos for visual cues at each step:

Step 1.

turn off your heating system













  • Turn your heating off so that the pump is not running. Turn off your heating system.


Step 2.

  • Once identifying which radiators are affected, wait for the radiators to cool so hot water doesn’t harm you whilst bleeding your radiator.
  • Wait for the radiator to cool down.

Time for radiator to cool down














Step 3.

what you need to bleed your radiator













  • The process of bleeding radiators can be quite messy, so to help with cleanliness and spillages you might need a cloth and towels. You’ll also need a radiator bleed key.


Step 4.

  • Starting with the ground floor radiators first.

ground floor radiators















Step 5.

  • Locate the bleed valve, which is usually at the top on one end. The ‘key’ should fit correctly over the square release nipple. Don’t turn anything yet. Make sure your work area is covered with towels and you have the clean cloth handy.

bleed valve















Step 6.

  • Carefully turn the bleed valve key (or if possible, a flathead screwdriver) anti-clockwise a quarter turn. Hold the dry cloth to the valve to soak up the water and try to protect the wall. You may hear a hissing sound until all the air escapes.
  • Note: If the whole bleed valve is turning at once, you will need to hold against the turning direction with a spanner as this will remove the vent plug and cause damage.

turn the bleed key














Note: If the whole bleed valve is turning at once, you will need to hold against the turning direction with a spanner as this will remove the vent plug and cause damage.

Step 7.

  • Once all the air has been released water will start to run out of the hole, wait for a steady stream of water without any spluttering. You can then close the valve in a clockwise direction.

release air from radiator















Step 8.

  • Make sure you clean up any spilt water, wiping down the radiator, so the radiator doesn’t rust. Cleaning the radiator is important here.

clean up radiator















Step 9.

  • Once you have completed these steps for all radiators in your system, you need to check that the pressure setting is correct on the system – if you have a Combination boiler.
  • Turn the heating back on and check all radiators for cold spots, leaks, and drips around the bleed valve. You may need to bleed some radiators again once the water has run through the system.
  • Turn the boiler back on

check radiator pressure














Step 10.

  • If you have a sealed pressurised system, check the manufacturers recommended pressure setting is correct. Normally 1.2 to 1.5 Bar.
  • By bleeding your radiators, the overall pressure will have been lowered. If the pressure is too low, you may need to top up your boiler with water.

We hope our step-by-step guide for bleeding radiators have provided some useful and comprehensive guidance on how to bleed radiators. Bleeding radiators is an important part of radiator maintenance and a way to ensure the efficiency of your heating. You don’t need professionals to do it, as bleeding radiators is a straightforward job to do yourself at home – we hope our guide on how to bleed a radiator has helped demonstrate that.

How do you bleed a radiator – FAQs

How to bleed a radiator without a key?

If you don’t have a key for bleeding radiators, then you can use a flathead screwdriver. Using one of these is a good alternative and will allow you to turn the small slot on the valve. However, at Stelrad we advise it’s best you get a radiator bleed key. You can get these in most DIY shops. Even though you can bleed a radiator without a key, it’s important to have the right tools in any case to ensure the valve is shut properly.

When to Bleed Radiators?

When to bleed radiators is a common question we get. In short, at least once a year – ideally twice. However, it’s also advised to bleed radiators after you have had any serious work undertaken on the heating system such as a replacement boiler or replacement radiators for example, or if you’ve had a radiator removed for decorating. Anything that may have necessitated having your heating system drained down.

Which Radiator to Bleed First?

Which radiator to bleed first is another common question. When you have two or more floors in your home, you always should start with bleeding the down stairs radiators first. Even though each radiator is drained as a separate entity as you go, starting on the ground floor is key. Once you’ve bled all the downstairs radiators you move on to the upstairs and so on. All the way to the highest point.

We don’t recommend that you bleed just one radiator – it may seem that one is cold more than the others, but you may be surprised how much air you manage to extract by bleeding ones that seem fine to the touch.

Can you bleed a radiator when the heating is on?

To avoid being scolded when water escapes from the radiator we advise you to switch off your central heating and let the system cool before you bleed the radiators.

How long does it take to bleed a radiator?

This can vary, depending on the amount of air that needs to be released from the radiator, the size of your radiator and whether you have all your kit ready. Typically, it takes 30 – 60 seconds for a radiator to be bled of air, but don’t be surprised if it’s a few minutes for large radiators, especially on older systems.

What does ‘bleeding’ radiators do?

It takes the unwanted air out of the system and allows the space the air was taking up to fill with water. This will help to ensure that you have the best possible water circulation in your heating system and a more efficient system.

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