How to bleed a radiator

How to Bleed a Radiator: 5-Step Guide – Housewarm

Last updated on February 22nd, 2024

Having air in your central heating system can cause a radiator not to heat, cold spots, and can even cause your boiler to stop working.

Your central heating system should be full of water at all times if you want it to heat properly and work as efficiently as possible.

I have been a full-time heating engineer for over a decade and have bled and fixed many radiators.

Bleeding Radiators

To bleed the air out of a radiator you need to find the radiator bleed valve.

This will be at the top of the radiator, usually on the right-hand side as most people are right-handed, but it could be on the left or the back of the radiator panel.

Bleed valve on back of panel
Bleed valve on back of panel

It is recommended to bleed radiators when the heating is off and the radiators are cold.

What’s needed:

  • A radiator bleed key
  • An old towel or cloth

Steps to bleed a radiator:

Step 1: Hold a towel under the bleed valve on the radiator to catch any water

Step 2: Place the radiator bleed key on the bleed valve screw

Step 3: Turn the key anti-clockwise slowly until you hear a hissing sound

Step 4: Keep letting the air out until water starts coming out then close the bleed valve

Step 5: Check the boiler pressure and top it up if it’s below 1 bar


How to bleed a radiator video

How to Bleed a Towel Radiator

Bleeding a towel radiator is the same process as a standard radiator. The problem with some towel radiators is sometimes finding the bleed valve can be difficult.

They put them in some strange places but usually, they are on the very top. It might be covered by a cap that needs to be pulled or screwed off first.

Bleeding towel radiator

How to Bleed Radiators With a Combi Boiler

When bleeding radiators with a combi boiler you will need to repressurise the combi boiler.

Every time you bleed trapped air out of a radiator, the pressure of the heating system will drop and you will need to increase the pressure.

A combi boiler boiler will not work if there is not enough pressure in your central heating system.

Low pressure gauge on combi boiler

How to Bleed a Radiator Without a Key

Bleeding a radiator without a key can be difficult and sometimes impossible, especially on old radiators.

Each situation and radiator is different. I will usually do whatever works for that setup.

Here are some of my ways to bleed a radiator without a key:

  • Use a screwdriver
  • Unscrew the bleed valve nut
  • Grip the bleed screw with water pump pliers
  • Use a socket set

Using a Screwdriver

Most modern radiators will have a bleed screw with a slot for a flathead screwdriver.

Using a screwdriver, you turn the bleed screw anti-clockwise using the screwdriver until you hear an air hissing noise coming out and close it when water starts coming out.

Bleeding radiator with screwdriver

Unscrewing the Bleed Valve Nut

Use an adjustable spanner or water pump pliers to turn the nut that the bleed screw is in.

Turn it anti-clockwise slowly until you hear the air coming out, then close it back up when the water starts coming out.

Adjustable spanner on radiator bleed valve

Gripping the Bleed Screw

Use some small water pump pliers to grip the bleed screw and turn it.

You might be able to use some long-nose pliers to grip the bleed screw and then grip the long-nose pliers with some water pump pliers as close to the radiator as possible.

Water pump pliers on bleed valve

Using a Socket Set

Use a small socket (usually 6mm) from a socket set and hammer it onto the bleed screw. Then use the ratchet to loosen the screw.

The socket should be slightly smaller than the bleed screw head.


Bleeding air out of a radiator is a simple task that everyone should learn how to do. It can help save money and heat your home properly.

If you have problems with radiators not getting heat or cold patches, the first thing you should do is bleed the radiators, then I would try balancing them.

Feel free to ask me any questions in the comment section below and I’ll try my best to help.

Please share this post if you find it helpful.


What happens if you bleed a radiator with the heating on?

Nothing happens if you leave the heating on but the hot water could potentially scald you (very unlikely).

As a heating engineer, I have to bleed hot radiators when the heating is on regularly.

The only problem for me is not having the accurate boiler pressure.

The pressure rises when the heating is on. You might need to top the pressure up when the system has cooled down if the pressure is too low. (below 1 bar)

Heating on temperature dial

How do you know if a radiator needs bleeding?

You will know if a radiator needs bleeding if the radiator is cold at the top, but hot at the bottom.

This is a sure sign that a radiator needs bleeding.

If the radiator isn’t getting hot at all, this could mean it needs bleeding, but it could also mean you need to balance the system or flush the radiator.

Why do I have to keep bleeding my radiators?

If you have to keep bleeding your radiators, that usually means water is leaking from your heating system.

This could be from anywhere on your system, including radiators, boiler, or anywhere on the pipework.

The most common place I find leaks on central heating systems is on radiator valves.

leaking radiator valve
leaking radiator valve


  • Steven Reid

    I am a full-time plumber and Gas Safe registered engineer. I incorporated Housewarm Ltd. in 2011 to provide heating and plumbing services to homes in Newcastle upon Tyne, England. I now blog about what I've learned over the years to help DIYers and plumbers.

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