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Witten by Bernard Morgan (Engineer) & Adam Apperley (Marketing). Published: April 18, 2023. Updated: February 15, 2024

How to Bleed a Radiator

Bleeding a radiator, a Boilerhut video guide :

Bleeding A Radiator

Bleeding a radiator at least once or twice per year is a requirement for most central heating systems. It is the process of removing trapped air from within the central heating system.

What does bleeding a radiator do?

It ensures that the system is up to full operating capacity, which can also increase energy efficiency.

Bleeding a radiator also ensures that your system continues to run at its maximum potential without putting strain on your boiler and increasing the cost of heating your home.

If you’re not sure how to bleed your radiators but have noticed that your home isn’t being heated as efficiently, we’ve covered all the details you need to know within this article.

Follow our step-by-step guide or contact Boilerhut for advice on troubleshooting an inefficient central heating system.

How do I know when my boiler needs bleeding?

Whilst it is recommended that you bleed your boiler twice yearly, some symptoms could appear that indicate that you might need to do it sooner.

Understanding and resolving these signs quickly will ensure you can keep your home warmer and reduce your bills.

  • Your Radiator Is Cold A The Top

    Realising that your radiators aren’t operating as effectively often isn’t a complicated process. Just by feeling sections of the radiator with touch, you will be able to identify if there is a temperature difference between the top and bottom of your radiator.

    A contrast in temperature will indicate that there is air in the system preventing hot water from flowing throughout the entire radiator. This is a telltale sign that your radiator requires bleeding.

  • The Whole Radiator Is Cold

    bleeding a radiator

    Again, just by touch, you can infer that your radiator needs bleeding.

    It is recommended that you allow the central heating system to warm up thoroughly before concluding that your radiator is cold.

    If surrounding radiators in adjacent rooms have become warm and the highlighted radiator has not, there is likely air in the pipes that need to be bled.

  • Rattling Radiators

    Perhaps one of the most apparent indicators of air within your radiator is an audible gurgling or rattling noise coming from within your pipes or radiators.

    The noise often sounds like a boiling kettle and occurs as the heating has been switched on. Once again, the sound is an indication of air within the heating system, bleeding the radiator in close proximity to where the sound originates is the most effective solution to release this air.

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How to Bleed a Radiator

Bleeding your radiator is a simple household task that doesn’t typically require the services of a plumber or a gas-safe engineer.

Following our step-by-step guide will provide enough detail to be able to bleed your radiators with confidence.

What You’ll Need

  • A radiator key OR a flathead screwdriver.
  • A jug
  • A piece of cloth
  • Safety-gloves

The equipment required to bleed your radiator can often be found around the home.

Radiator keys can be substituted for a flat-head screwdriver or can be purchased for just a few pounds at most local DIY stores.

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Below is our step-by-step guide on bleeding a radiator:

  • Turn your central heating on

    Before determining whether or not your radiators need bleeding, it is essential to assess which radiators hold built-up air.

    Ensure that before deciding which radiators to bleed, you wait for the heating to fully circulate your home.

  • Identify Cool Spots

    Once your radiators are fully heated you can assess the temperature of your radiator from top to bottom.

    However, it is vital that you take caution during this action. If your radiators are too hot, you can wear thin gloves to prevent injury or discomfort.

    Identify whether any radiators are colder at the top or aren’t as warm as others.

  • Turn Off Heating And Wait For It To Cool

    It is vital to allow a considerable amount of time for your central heating to cool down.

    If you attempt to bleed your radiators before allowing the central heating to cool, you could scold yourself with steam and boiling water escaping from the radiator.

  • Protect The Area Surrounding Your Radiator

    With a cloth or towels, create a protective area surrounding the radiator to prevent water from reaching the carpet or walls.

    You can also use a jug or bowl to catch excess water that escapes from the radiator.

  • Open Te Bleed Valve

    Using your radiator key or flathead screwdriver, release the bleed valve on your radiator.

    The valve typically requires turning once or twice anti-clockwise. You will know when the valve is open once you hear a hissing sound. This sound indicates the air escaping your central heating system.

    99% of the time there is only one bleed valve, but this bleed valve will always be at the top of the radiator.

    If it’s a vertical radiator, assess the height risk.

    Also, not all bleed valves have a screwdriver slot, but all modern bleed valves do.

    • It is not unusual to witness a strong smell when releasing stagnant air from a radiator. This is methane and can be highly flammable.
    • Make sure both radiator valves are open and Thermostatic valves adjusted to maximum whilst bleeding .
  • Close The Bleed Valve

    Your radiator should only require bleeding for up to 20-30 seconds, depending on how much air has built up in your system.

    Once the hissing sound starts to gurgle, or water begins to escape from the valve, you know it is time to close it.

    This can be closed by turning once or twice clockwise, in the opposite fashion to how it was opened.

  • Turn The Heating Back On

    After bleeding the radiators in your home, it is a good idea to turn the heating back on to check a couple of things. The first is to ensure that your boiler pressure isn’t too low.

    Occasionally, allowing too much water to leave the central heating system can create lower pressure. This will require you to repressurise the system.

    Secondly, if your boiler pressure is correct, check whether your radiators are fully heated.

    If cool spots persist, this could be an indication of more complex problems. Under these circumstances, you might need a Gas Safe Registered Engineer to professionally diagnose and resolve the problem.

    The team at Boilerhut are certified and determined to help you heat your home without any fuss, visit our website to receive professional assistance with your boiler.

Final Thoughts

Cold or noisy radiators could be a sign that air has accumulated within your central heating system.

The air gathers within the top sections of your radiators, preventing them from efficiently heating your home.

Bleeding your radiator is a quick and straightforward fix for this problem, allowing you to complete the task without the help of a boiler expert.

In addition to some simple preparation, bleeding your radiator should only take around 30 seconds. After this, your home will heat far more efficiently.

Once you’re done with bleeding your radiator, it is a good idea to repressurise your boiler, especially for a Sealed System or a Combi Boiler.

The video below may help >

If any problems persist after bleeding your radiator, this could be an indication of more complex problems.

Under these circumstances, you’ll likely require the services of a Gas Safe Registered Engineer.

Boilerhut only employs Gas Safe Registered and manufacturer trained engineers across the UK to provide complete peace of mind and a fully functioning boiler.

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