How to Bleed a Central Heating System


When air becomes trapped in your central heating system, it can noticeably reduce the thermal output of your radiators. Air can get into the system when it is topped up with water, so you need to know how to bleed your central heating system.

Things You'll Need

  • Cloth
  • Switch off the central heating system. The switch or valve will be in the main body of your central heating system unit, but its exact location differs depending on the model. Refer to the manual for your particular system and switch off the system.

  • Locate the bleed valve on your radiators. The bleed valve is usually at the bottom of the radiator and is usually a knurled release handle. If this is the case, you will not need any special tools to bleed the central heating system.

  • Gently wrap an absorbent cloth around the bleed valve. Water may dribble from the valve when you turn it; the cloth will absorb the water and stop it from leaking all over the room.

  • Turn the handle counter-clockwise to open the bleed valve. Do this gradually and gently. As the valve begins to open you will hear a hiss of air; this indicates that the bleeding process is successfully expelling trapped air.

  • Close the valve when water begins to bleed from it. When water begins to dribble out, it means you have expelled all the excess air and you are now getting rid of valuable water. Turn the handle clockwise to seal the valve.

Tips & Warnings

  • It is advisable to wear gloves when bleeding the system, as the water may be hot.

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  • Photo Credit white radiator image by Ekaterina Sidorenko from
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