View our step by step guide

How to bleed a radiator

If you've noticed that your radiators aren't as hot as they should be, or that it's taking longer than usual to warm up your home, it could be because bubbles of air are trapped in your heating system. These pockets of air can stop the hot water in your radiators from circulating properly, reducing their efficiency and the heat they put out. Fortunately, bleeding radiators – which means releasing the trapped air – is a simple job that you can do yourself. If you want a warmer home, lower energy bills and a more efficient heating system, you can learn how to bleed a radiator by following these steps.

1. Check the top and bottom

While the heating's on, carefully touch the radiator along its top and bottom to compare the heat. Trapped bubbles of air tend to rise upwards and collect at the top. So if your radiator's cold at the top and warm at the bottom, this could be a sign that it needs bleeding.

2. Get your tools ready before you begin

You should find everything you need for bleeding radiators at a DIY shop. You might have most of it lying around the house already. But before you start, make sure you've got:

  • a dry cloth
  • a radiator or air key
  • a small container to catch excess liquid
  • and some protective glasses and gloves.

3. Turn off your heating

There's usually a small amount of water that'll escape when you bleed the radiator, and you don't want it to be hot when it does escape. So turn off your heating, and let the radiator cool down before you do anything else.

4. Find the bleed valve

On the side of the radiator, near the top, you'll find a square section shank. This is the bleed valve, and your radiator key should fit neatly onto it. Place your container on the floor directly underneath this valve, ready to catch any drips of water later on.

5. Use the key to let out the air

Put on your protective glasses and gloves, and hold a dry cloth underneath the bleed valve so you're ready for any drips. Fit the radiator key onto the shank of the bleed valve and slowly turn it anti-clockwise – about a quarter of a turn. You'll hear a hissing noise as the air escapes.

6. Be ready to close the valve again

Keep the radiator key fitted to the bleed valve so you're ready to close it straight away. When the hissing stops and water starts to dribble out of the bleed valve, turn the key clockwise. This will close the valve, stopping any more water from escaping. Wipe any excess water from the valve and the radiator, and make sure you've closed the valve tightly.

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