How to Bleed a Radiator

Last updated: August 30, 2016


Bleeding a radiator is quite simple and is something that you’ll probably have to do every now and again to ensure that your central heating is operating at the best level possible.

Over time air can build up in radiators causing them to be colder at the top than at the bottom – this is when knowing how to bleed a radiator can come in handy.

This cold-spotting on your radiators makes your heating system much less efficient, meaning it has to work harder to heat your home to the required temperature – resulting in higher energy bills and a larger carbon footprint.

This problem can be very easily fixed by bleeding the radiator to remove the air. Watch the video guide below or alternatively follow the simple step-by-step instructions on how to bleed your radiator.

What Does ‘Bleeding a Radiator’ Mean?

To bleed a radiator is to release air that has become trapped inside. This is done by opening a small valve on the radiator known simply as the ‘bleed valve’ or ‘bleed screw’. The trapped air stops hot water flowing through all parts of the radiator, so it’s important to make sure you remove this air in order to ensure your radiator is operating at maximum capacity.

Do I Need To Bleed My Radiator?

You will need to bleed your radiator if it is colder at the top than at the bottom, if it is cold all over or if it is colder than it should be according to your heating settings. Air in the system can also cause knocking sounds in your pipes, so if you begin to hear noises that you wouldn’t normally expect, it may be worth checking each of your radiators for any of the symptoms mentioned.

If you are experiencing the following problems –

  • All radiators are cold
  • Radiators on the upper floors are cold
  • Radiators have a build-up of water underneath them

– then bleeding your radiator may not fix the issue and the cause may be a larger problem with your heating system such as complications with the pressure or radiator leaks. If this is the case, it is advisable to contact a professional.

Another benefit of radiator bleeding is that it makes sure your heating system is working efficiently thus reducing your energy bills.

How Do I Bleed A Radiator?

Firstly, before you can start bleeding your radiator, you will need a few tools:

  • A rag
  • A small container or a bucket
  • A radiator key or flat-headed screwdriver (if you can’t find your radiator key then you should be able to purchase a replacement at your local DIY store.)

rag and container for bleeding a radiator

a radiator key

NB. BestHeating recommends using a radiator key where possible to avoid damaging the bleed valve.

Step 1

checking radiator is cold

Ensure your central heating system is on and running. Check each of your radiators at home and see if all parts are warming up. This will give you an idea of which radiators you need to bleed.

Air tends to get trapped in the highest radiators in your house so be sure to inspect those on upper floors.

Step 2


Make sure you turn off your central heating system and allow plenty of time for it to cool down before you begin to bleed your radiators.

Step 3

container below radiator bleed valve

At one end of the radiator, at the top, you’ll find a bleed valve. Put your container on the floor under the bleed valve to catch any water when you begin to bleed your radiator.

The bleed nipple should have a small water outlet at the bottom. If the nipple has an incision running across the middle then it is safe to use a screwdriver to open it.

Step 4


Using your radiator key (or screwdriver), turn the bleed nipple anti-clockwise and you should hear a hissing sound. This is the trapped air being pushed out by the water pressure. Opening the bleed valve allows cool air to escape, which is then replaced with liquid from your heating system.

Step 5

water starts to bubble from the bleed nipple

Once water starts to bubble from the bleed nipple, use your rag to catch the water. Be careful at this point as the water may start to spray. Once all the air is out, turn the bleed valve to close.

Step 6

finished bleeding radiator

As water has been released from the system you will probably find that the pressure has dropped on the boiler. Check the pressure by looking at the gauge on the front. To optimize the pressure, the gauge pointer usually needs to be between one and two bar.

If it’s too low you will have to refill it using the filling loop – there’s more info on how to refill with a filling loop in this handy little video.

On open-vented systems (automatic), the system will refill itself so you should be good to go.

How Often Should I Bleed My Radiator?

Generally speaking you should really only bleed your radiators and heated towel rails when your radiators start to feel colder at the top or begin to develop cold-spots. However, some professionals have suggested bleeding your radiators annually and after any modifications, services or repairs.

If you’ve got any burning heating issues or need advice from the experts, be sure to send in your questions. We may feature them in our next blog post, too. Questions can be sent via the comments section below, Facebook or Twitter.