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How to bleed a radiator

By Tom Drake | 13th June 2023 | 4 min read

Learn how you can bleed your radiators to keep them working at their best

Bleeding your radiators is an important part of central heating maintenance that will keep your system working at its best. In this guide, we take you through how you can bleed your radiators and why it's so important.

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What is radiator bleeding?

Over time, air can become trapped inside radiators that will prevent the water circulating. Bleeding your radiators will remove this trapped air.

Why do I need to bleed my radiators?

When there's air trapped in your radiator and the water can’t circulate properly, your room will take longer to warm up. This means higher energy usage and as a result, higher bills.

How do I know if I need to bleed my radiators?

If your radiators are cold at the top but warm at the bottom, this will usually mean you need to bleed your radiators. As water is heavier than air, the trapped air will always be at the top of the radiator. This prevents warm water reaching this part of the radiator so it will feel cold.

Gurgling or banging noises coming from your radiators are also a good indicator that there’s air trapped in the system. Lastly, if you’ve noticed a general drop in the performance of your radiators over time, it’s likely they need to be bled.

How to bleed radiators:

  1. Turn off your heating system
  2. Fit the bleed key
  3. Turn the key to release air
  4. Close the valve
  5. Repressurise your system

1. Turn off your heating system

First, you need to identify which radiators need to be bled. You can then switch off your heating system and let your radiators cool down. As water will be released when you’re bleeding your radiators, you want to make sure any water in the system isn’t hot.

2. Fit the bleed key

Locate the bleed valve on your radiator. The bleed valve is a small metal square inside a white round nut that will usually be located on the side of your radiator. If you’re unsure whether you've found the bleed valve, all you need to do is check if your bleed key fits.

3. Turn the key to release air

Grab an old towel or container and hold it underneath the bleed valve. Fit your key to the valve and turn it half a turn, you should start to hear air coming out of the radiator.

Releasing water from a radiator bleed valveReleasing water from a radiator bleed valveReleasing water from a radiator bleed valveReleasing water from a radiator bleed valve

4. Close the valve

Keep the valve open until air stops coming out and it’s just water being released. At this point you’ve successfully released the air from the radiator and you can close the valve again. Be careful not to over-tighten the valve as this could damage the thread.

5. Repressurise your heating system

If you have a combi boiler, check the pressure of your heating system after you’ve bled your radiators. Radiator bleeding can cause the pressure to drop and if this occurs, you’ll need to top up the pressure.

How often should I bleed my radiators?

It’s recommended that you bleed your radiators once a year. It's a relatively quick and easy piece of central heating maintenance that can make a big difference to the warmth of your home.

That concludes our guide to bleeding radiators. This is a job that can be done in less than an hour and will really help your heating system function at its best.

If your radiator is cold at the bottom, take a look at our guide to fixing that issue or if you’ve bled your radiators and you’re still not getting the best heating performance, it might be time to invest in new radiators.

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