How to Bleed a Radiator

When the cold winter months strike it’s time once again to get reacquainted with your home’s best friend: the radiator. Since it’ll be keeping everyone warm it’s important to make sure it’s working in optimum condition. But if not, the problem might be a simple one to fix by bleeding the radiator. If you’ve never bled a radiator don’t worry, the process is fairly simple and doesn’t take long. To find out if your radiator needs bleeding and how to do it if it does, then read on.

While the term bleeding a radiator conjures up a process that involves some kind of liquids, it actually doesn’t (although small amounts of water might be involved). It refers to simply letting air out of the radiator that has become trapped inside. That trapped air is preventing the hot water from getting to parts of your radiator (usually the top), which means it’s not heating up all the way. To make the device completely energy efficient, it’s important to make sure the entire radiator is heating up.

The first thing to do – especially if you have more than one radiator – is to turn them all on. If they are tied to a thermostat that controls more than one radiator, then make sure it’s turned up high enough to force all the radiators in the home to heat up. Next, check each radiator to see if every part of the unit is warming up while staying careful not to burn yourself since they can get very hot. Any cool spots – especially near the top of the radiator – most likely means there is air trapped inside and the radiator needs to be bled. In extreme cases of trapped air, the entire radiator will be cool which will contrast with the rest of your central heating system in which other radiators will be hot to the touch.

If you encounter a problem like the ones described above, it’s time to bleed the radiator. If not, then the radiator is working fine and there’s no need for further action. As mentioned, bleeding a radiator is a simple process that’s also safe to do on your own.

    1. Before starting the bleed process, turn off all the heating so you do not to import any more air into the system and insure that you’re working on a fully cooled unit to prevent any burns.
    2. The first thing needed is a radiator key or bleed key as shown below. Most radiators come with this device. With more modern radiators, a flathead screwdriver can be used in its place.
    3. At the top of the radiator on one end, there will be a valve that you can attach the key to. Have a cloth and/or small bowl ready to catch any water to prevent spills on the floor.
    4. Fit the radiator key into the valve and carefully turn it counter clockwise a small amount; just a ¼ or ½ turn should do the job. You’ll hear a hissing sound, which is the air escaping, and when that passes, water will either dribble out (or emerge as a jet in more modern radiators).
    5. Use your cloth to catch any water and then immediately turn the valve clockwise back to the closed position, as the bleeding is now complete.
    6. Once this process is done, turn the heat back on to check that there are no leaks from the radiator valve and to confirm that the entire radiator is now heating up and working properly.
    7. Follow this process on all other radiators that require bleeding.
    8. If your heating system is running on a combi boiler then ensure the pressure on the boiler has not dropped below manufacturers requirements (usually between 1-1.5 bar).

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