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How to know if your radiator needs a bleed?

If your heating is on, but your radiator is cold, you may have trapped air inside the radiator. Depending upon the severity of the problem your radiator will probably be hot at the bottom, but cold at the top. This happens when air pockets form in the radiator, rising to the top and taking the place of the hot water that should be there.

Bleeding a radiator means letting out the trapped air inside your radiator for it to function efficiently.

You do not have to call for professional help for this task as it is relatively easy and could be done at home by yourself following our simple 10 step guide on how to bleed a radiator.

How To Know If Your Radiator Needs A Bleed?

If you have a problem with just one radiator (or a few) then the most likely explanation for the issue is trapped air. You might observe a cold spot at the top of the radiator or a gurgling sound when you turn the radiators on. That’s a critical sign that you need to bleed the radiator.

What Will You Need To Bleed A Radiator?

Bleeding a radiator is not a difficult task that will cost you a good chunk of money. You will need some handy tools that you will most probably find around your house, i.e.:

  • A Radiator Key (can be bought from any DIY store or a supermarket)
  • A towel or cloth to prevent any water from spilling around
  • A pair of gloves

Let us get going on the steps of how to bleed a radiator now

Before bleeding your radiators, you must check all your heating systems and check that everything is functioning as it should. For that, you need to turn on your central heating system for a good time to let the radiators get warmed up well so that you can detect which radiator needs a bleed.

You might consider bleeding all the radiators simultaneously. Still, it is highly recommended to bleed those radiators that are blocked up with excessive air, or you might end up releasing extra pressure out of the system that is needed for the heating system to perform effectively.

Once you have allowed the radiators to heat up, you need to feel the top of each radiator cautiously. There should be a nice even temperature across the whole radiator. Also, listen for any unusual noise your radiators make or the time your radiator takes to heat up. If the radiators make any such sounds or take extra time to get heated up, then it is likely that your radiator needs to be bled.

Once you are done analyzing which radiators need a bleed, turn off your central heating system and allow all the heating apparatus to cool off. This step might be time-consuming, but it is extremely important that you follow this step for your safety as bleeding radiators still steaming hot can spurt out bubbling water or blazed air that could damage your skin.

After your central heating system has cooled off, you need to prepare the area around your radiator to prevent any spilling of water or to get any stains on your floor or carpet as old radiators tend to leak some stained water. Grab a cloth or towel and spread it around your radiator and keep a towel in your hand to hold it around the bleed valve for extra caution.

Most radiators have a bleed valve at the top corner on either side that looks like a hole with a square inside it. If you are unsure about the bleed valve, then refer to your radiator’s manual to find the valve.

Grab your radiator key or screwdriver and turn the bleed valve just a quarter anti-clockwise. You should hear a hissing sound that confirms that the air is escaping the radiator.

Do not loosen up the valve completely or too much as that might lead to excessive water spillage, which could be a problem for you to clean.

You need to let the radiator bleed until you stop hearing the hissing sound and observe a steady flow of water through the valve. Do not be confused if you see water dripping as soon as you loosen the valve as the radiator might let out some water along with the air. The key sign that you are looking for is steady water flow and not distorted droplets with air. When you observe that sign, turn the valve back to its place. Repeat the same process with all the radiators. Be vigilant to tighten the valve as soon as you observe the sign to prevent excessive water spurt.

A bleed valve releasing water from the radiator.

After bleeding, check your boiler’s pressure before turning on the heat. The pressure might have dropped because of air escape; hence you would need to top up the boiler pressure.

The regular reading of the boiler pressure while turned off should be between 1-1.5 bar. If it is below this, you need to supply the boiler with more pressure by filling it up with water via an external filling loop until the pressure reaches the required reading.

Run the heating system back on to check if your bleeding was effective or not. Wait for the radiators to get heated up and make sure all your radiators are heating up efficiently without having any cold trace over their bodies.

If you still feel that your radiator is cold, it might need bleeding once more. If, even after multiple bleeding, your radiator does not warm up fully, there might be a more complicated issue with your boilers, such as a sludge blockage or leaking pipes.

Now that you know how to bleed a radiator, you need to be aware that radiators need a balanced check every few months to avoid any disruptive behaviour in the heating process, which could eventually affect the lifespan of the radiator.


In a nutshell, this is the checklist of what you need to do:

  • Turn on the heating system
  • Analyse the radiators
  • Turn off the central heat supply
  • Prep the area around the radiator
  • Locate the radiator bleed valve
  • Loosen the bleed valve
  • Wait while the radiator bleeds
  • Check the boiler pressure
  • Turn on the heating system again

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