How to Bleed a Radiator : Step-by-Step Walkthrough

Tuesday 11 October 2022

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After a very warm summer, the days and nights are getting colder. Your home is most likely feeling it too. It’s time to switch on the central heating, but after months of not being used, it’s fairly common for radiators not to warm up, or only doing so partially (cold at the top and warm at the bottom). 

This is due to air trapped in pockets becoming trapped inside the radiator. If that is the case, then you may need to bleed your radiators. This is a key part of radiator care but is one that a lot of people dread or simply avoid as it seems such a daunting task.

However, once you see how easy it can be, it’s much easier to attempt and then keep on top of each year. Taking the first steps is often the most intimidating but there’s really nothing to be worried about.

In this quick, easy and straightforward guide, we will give you a step-by-step on how to bleed a radiator. Just make sure you follow these guidelines closely and you’ll have no problems at all.

Top tip: If you’re bleeding multiple radiators in your home then it’s best that you start with the one that’s furthest away from your boiler. If you live in a home with two or more storeys, you should start with the downstairs radiators, before repeating the process upstairs. This means you won’t be dealing with different pressures along the line affecting your hard work. 

Before you start, you’ll need to source a radiator bleed key. These are simple, common tools available from DIY stores or you may have one floating around in a toolbox. They are generally a hollow-tipped butterfly design and once you’ve located one, keep it in a safe place so that you can repeat this process every year. 

  1. Turn off all the radiators in your home and ensure that they are cold. You don’t want to be sprayed with hot water or have to deal with minor scolds. Pick a warmer autumn day to get started.
  2. Locate the bleed valve – often found on the side of the radiator – and place an old cloth or rag just under it (this is because a little bit of water will leak out during bleeding and you don’t want to ruin your flooring). It may be worth putting a towel down or a drip tray if you haven’t done this in a while or have never tried to bleed a radiator before. 
  3. Insert the bleed key into the valve. Have a firm grip and treat it like turning an Allen key or screw, use your whole arm as support, not just your wrist.
  4. Turn the bleed key anti-clockwise until you open the valve and air starts escaping (you should hear a hissing noise, this is completely normal).
  5. Water will start to escape from the valve. As soon as this happens, turn the bleed key clockwise to re-tighten and close the valve. If you’ve hit water, the radiator has been bled effectively. Your aim is to get rid of the air so that your radiator is completely full of water.
  6. Repeat this process on all radiators that require your attention (remember to start with the radiator furthest away from the boiler). 
  7. Turn your heating back on and check if your radiators are now heating up correctly.

And there you have it! It’s really that simple. If problems persist, then you may need to call a plumber to take a look at your boiler or central heating system and radiator maintenance. 

If your radiators are cold at the bottom but hot at the top, you may have some silt, sludge or other blockage in your pipes. This is a bit more serious and you’ll need someone qualified to flush or drain your system, it’s best to hire professional services to do this.

If your heating is turned on and other radiators are working fine, but one radiator is refusing to heat up, you may have some stuck or frozen valves. This will be stopping water from getting into the radiator at all. This could also be a blockage from sludge and impurities in the water. 

In some cases, there may be a bigger problem going back to issues with your boiler. In these kinds of situations, we recommend you ask a Gas Safe registered engineer to intervene or at least investigate. You might need to have your central heating system power flushed which is a more costly job.

Remember, noisy radiators are generally not a problem. If you hear clicks or creaks this is completely normal, it will simply be a radiator expanding due to heat slightly. The same can be said for piping under floorboards. If you find a radiator hissing or the sound of air, just make sure you finished the bleeding properly and close the bleed valve tightly.

Any leaks need to be dealt with by a plumber, if you can, switch off the radiator valves that feed the water and lay down some trays to catch any leaks. This may have been caused by corrosion or age and is best dealt with right away.

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