Homeowners Professionals

How to bleed a radiator

Bleeding your radiators is a necessary job if you want to keep your heating system running efficiently and ensure your home is nice and warm. Air can become trapped in the system, interfering with how much heat your radiators can put out, and it needs to be removed. Keep reading to find out how to bleed your radiators.

Bleeding your radiator in 6 steps

Below, you can find the basic steps on how to bleed a radiator yourself. Keep reading to find more detailed information and expanded steps to follow.

  1. Turn your heating off and allow time for it to cool down
  2. Take a towel and a jug and place both underneath the bleed valve on the radiator
  3. Insert the bleed key and turn it slowly, anti-clockwise
  4. Air will escape and you will hear a hissing noise. Close the valve when water starts to come out
  5. Repeat on all the radiators in your home
  6. Turn your heating back on and check the radiators are heating up properly.  

Top Tip: when bleeding multiple radiators, start with the one furthest away from your boiler, as it likely contains the most air.

What does bleeding a radiator mean?

Bleeding a radiator is the process of removing any excess or trapped air within the system. Air cannot be heated in the same way as water, so it is usually the reason why a radiator feels cold at the top.

The air rises and becomes stuck, so the hot water can only reach about halfway up the radiator. This is highly inefficient and may help to explain why you’ve been experiencing cold spots or draughts in your home, or generally wondering why a room feels a little chilly.

Bleeding your radiators isn’t the same as flushing a system - you’re not removing the water, just letting the air out.

It’s a process that takes just a few minutes, but could improve the efficiency of your heating system and make your home a little toastier. 

How do I know if my radiators need bleeding?

You will know if your radiators need bleeding because you may feel a cold spot, or they may take a long time to heat up. They might also make gurgling noises when the heating comes on, which is usually the air moving around in the system.

If you’re unsure, you can try bleeding one radiator to see how much air is in there. You’ll know when all the air is out because the hissing noise will stop and water will appear instead

What tools do I need to bleed a radiator?

You only need very basic tools to bleed your radiators, and these are:

  • A jug or tray to catch any excess water
  • An old towel
  • A radiator bleed key.

If you don’t have a radiator bleed key, you can read our handy guide on  how to bleed a radiator without a key.  

How to bleed radiator video

How often do I need to bleed my radiators?

Bleeding your radiators is a job that should be done at the start of every winter, when you turn your heating on for the first time in many months.

While the heating has been off, it’s likely that air has built up in the system, so removing it now is the best thing to do. Keep your heating system running efficiently by repeating the job annually. You may also wish to check your radiators regularly to see if they need bleeding throughout the winter.

When radiators regularly get cold spots, trapped air may not be the problem. Cold spots can be caused by dirt and rust that builds up over time, but can also suggest there is a leak in your system.

In this instance, check around your boiler and underneath any radiators for obvious signs of a leak. If there is no leak, your  system may need flushing  to remove all the dirt stuck inside it.


  • Trapped air can cause cold spots
  • The air can be removed by bleeding your radiators
  • You can bleed each radiator one at a time using a radiator bleed key
  • Do this job at least once a year to maximise the efficiency of your heating system.
  • If you bleed your radiator you may need to  top up your boiler pressure
How can we help?