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Getting ready for winter - Why are my radiators cold?

top of a radiator with a TRV on the end in a bathroom

If you notice your radiators are not heating up properly or you can hear some unusual sounds coming from the system, it could suggest that your radiators need bleeding.

Bleeding your radiators just before we head into the colder months is a great way to make sure your heating system is performing efficiently.

Why bleed your radiators?

If your radiators aren’t heating up to your desired temperature, heating up unevenly or you can hear a strange bubbling or clunking noise, this might be because of air that’s trapped inside. By bleeding your radiators, you are releasing the trapped air meaning the heat can flow more freely and heat your home. You can bleed your radiators yourself is a few easy steps. Read our guide here.

bottom of a radiator

What's the impact of air in the system?

If your radiators are full of air, it can prevent the hot water reaching all the space inside. You could have your heating on full blast, but if it’s not spreading evenly through your radiators, your system will be working harder than necessary to try and heat your home, meaning you are wasting energy which could result in higher heating bills.

When should you bleed a radiator and what do you need?

Some of the signs to look out for that suggests you should bleed your radiators are when you put your heating on and your home is still cold or if you hear a bubbling sound when you first turn your heating on. Another thing to check is when you touch your radiators and if you notice that they are hot at the bottom but cold at the top, it can also suggest there is air trapped in the system.

In order to bleed your radiators, you need a radiator key so you can open the valves on your radiators – you’ll be able to buy one of these from most hardware stores. Some valves may only need a flat head screwdriver, so double check the shape of the valve before starting. You will need a bucket or bowl to collect any water and a cloth can be handy to clean up. Sometimes the water that comes out of an old radiator can be discoloured, so of you have light-coloured carpets, make sure to cover them to avoid any damage.

  1. How to bleed a radiator
  1. 1

    First, make sure your heating is switched off and give it some time to completely cool down, including pipes and radiators.

  2. 2

    Next, place the radiator key or screwdriver on the radiator valve. Have your cloth on standby in case you need to wipe up any drips.

  3. 3

    Turn the key or screwdriver slowly anti-clockwise to begin releasing air from the radiators. You will hear a hissing noise as soon as air drops out of the radiator – a quarter turn should be enough but listen out anyway.

  4. 4

    Let some of the heating water run out of the radiator and once this stops place the radiator key or screwdriver in the valve and close it by turning it clockwise

  5. 5

    Turn on your heating and give your radiators time to heat up. By releasing excess air from the system, you may get a low pressure warning on your boiler or notice your pressure gauge is below 1 bar. If this is the case, we’ve prepared a handy guide to show you how to top up your system pressure. Click here to find out more.

How long will it take and how often should they be done?

How long it takes to bleed your radiators depends on the number of radiators in your home and the amount of air in them. It’s estimated that it should take 30 seconds to a minute for each radiator. For each radiator that you bleed, you should wait until water starts to come out of the radiator before closing the valve back up. This means that the water has risen to the top of your radiators as the trapped air has been released. You should check every radiator in your home to see if they also need balancing before switching your heating back on. Speak to your local Vaillant installer here.

It’s recommended to only bleed your radiators if they are cold in certain areas when the heating is on. There’s no need to do it on a regular basis as you could open the valve to just release water which could get on your walls and floor.

If your radiators still feel cold after bleeding them, it may be that your central heating system needs flushing. This must be done by a heating engineer.

Is your heating system still not working properly?