How to Bleed a Radiator: A Quick & Simple Method

Bleeding a radiator using a bleed key
29 September 2023 2810 view(s) 3 min read
How to Bleed a Radiator: A Quick & Simple Method

If your radiator takes longer than usual to heat up, is noisy, or isn't hot from top to bottom, it may require bleeding.

It is very normal for air to build up in a radiator over time, but when these pockets of trapped air are left, the hot water cannot circulate properly preventing a radiator from running efficiently and effectively. With air having a far lower density than water, it sits at the top of the radiator, which is why a radiator will feel cold at the top and still warm at the bottom.

Bleeding your radiator serves to release this trapped air, thus allowing the hot water to circulate properly and the radiator to heat up as it should. In this quick guide, we will guide you through the various steps involved in how to bleed a radiator. 

What You’ll Need to Bleed Your Radiator

In order to bleed your radiator, the following tools will be required:

  • Radiator bleed key or flathead screwdriver - A bleed key is a particular tool specifically designed to fit a radiator bleed valve. Alternatively, if you don't have one of these to hand a flathead screwdriver would serve the same purpose.
  • A container such as a washing-up bowl - To be placed under the radiator as you are bleeding it to catch any excess water escaping.
  • Rag or towel - Useful for catching any water that may escape as you bleed the radiator.


1. Before starting to bleed a radiator, remember to turn off the central heating system and then wait for the radiator to completely cool down.

A white thermostat hanging on the wall

2. Locate the bleed valve at the top of the radiator - this can be at either end.

3. Place your rag or towel just below the valve and your container underneath the radiator below the valve. This is to prevent the water that will come out from damaging the wall or flooring. Be aware that on some valves there is a tiny outlet, which could be positioned anywhere - so make sure to have a proper search for one, or you could end up with a messy wall.

4. If you’re using a bleed key it should fit over the vent similar to an an old clock key, whereas a screwdriver will fit into the groove. Once engaged, slowly turn the vent anticlockwise until you hear a hissing sound (this is the trapped air escaping.

5. Keep the valve open until the hissing stops and only water comes out, then quickly close the valve and retighten it.

6. Repeat these steps for any other radiators that need bleeding.

7. Turn the central heating system back on and remember to check if the radiator/s are now heating up properly – evenly, quickly and with no noise.

If bleeding the radiator doesn’t improve or solve any of these issues, especially if you’re bleeding it frequently, it is likely that there may be a more serious issue that should be looked at by a heating professional.

Previous article:
Next article: