Bleeding a radiator

Summary: Learn how to bleed radiators, bleed a radiator to let the trapped air out.

If you find that your central heating system isn’t warming your property as well as you would like, you may need to check that all of your radiators are working properly. If you come across a radiator that is warmer at the bottom than at the top, you have a radiator that has trapped air, preventing the water to flow freely. You will need to bleed the radiator in question, which is a process that allows the excess air to be released from the system.

How to bleed a radiator

  • Firstly you will need to have access to a bleed key.
  • Start by turning off your central heating as this prevents more air entering the system.
  • Find the bleed valve, a square shaped lock at one end of the radiator near the top.
  • Hold a cloth underneath the valve to catch any leaking water and slot the key onto it. Use the key to open up the valve until you start to hear air hissing out. The sound is like that of a bicycle tyre being deflated. You do not need to turn the valve very much for this to happen.
  • When the valve starts to dribble water, you have removed the problem air from the system. Now you can tighten the valve again and wipe away any dribbled water. Be careful as the water may be scalding hot.
  • You may now turn your central heating back on.
  • If you find that you have to bleed the radiators more than once a year, then you may need to seek help from a plumber. If air is in your system too much, it can cause corrosion.

Very gently open the bleed valve until a small amount of water dribbles out.