How To Bleed A Radiator

How to bleed a radiator is a question that is asked when a central heating system is not working properly.

Bleeding a radiator releases air trapped inside a central heating system.

Air in the central heating system causes radiators to be cold at the top and warm at the bottom. Pockets of air prevent individual radiators from getting hot.

Bleeding a radiator is a simple task that does not require plumbing knowledge. You will need a radiator bleed key, cloth and bucket to bleed the radiator.

To bleed your entire central heating system you simply repeat the process for each radiator in a specific order.

bleeding radiators

Step-By-Step Guide To Bleed A Radiator

To bleed a radiator you will need a radiator bleed key, a cloth or jug.

  1. Your central heating needs to be switched off and the radiators cold.
  2. Place an old cloth or a jug under the bleed valve
  3. Insert the bleed key into the radiator bleed screw
  4. Slowly turn the bleed key anti clockwise until you hear hissing sound
  5. Turn the bleed key clockwise to close the bleed screw when the hissing sound stops and water comes out of the radiator.

If one radiator needs bleeding you should bleed the entire central heating system.

How to bleed a central heating system

To bleed a central heating system you should bleed all radiators following these rules:

  • Ensure the central heating is switched off and cold before staring the process.
  • Start by bleeding the radiators furthest away from the boiler.
  • If the property is on multiple floors, start at the lowest point and work your way up the property.
  • Once the process is complete restart your boiler and turn the heating on.



radiator bleeding key

When To Bleed Radiators?

Understanding when to bleed your radiators is important to ensure your heating system is working properly. Our advice is to bleed radiators at least once a year, although you will likely see improvement if bleeding them more frequently.

When you bleed radiators regularly, you’re not only ensuring a sufficient hot water supply but are prolonging the longevity of your heating system.

Here are a few signs that may indicate it’s time to bleed a radiator:

  1. Cold spots are a classic sign of trapped air. If the top of your radiator is colder than the bottom, your radiators need bleeding.

  2. Gurgling noises indicate pockets of air within your radiator. If you hear gurgling or bubbling sounds, you need to bleed your radiators.

  3. Delayed heating is another sign of blockages that hinder the flow of hot water within your radiator. If your radiator is taking too long to heat up, it’s time for radiator bleeding.

  4. Increased heating bills indicate a problem with your heating system. Trapped air reduces the efficiency of radiators as it limits the flow of hot water. As a result, your radiator needs to use more energy to heat the water, causing a spike in energy bills, costing your more money everyday.

  5. In severe cases, your central heating system may not work at all when there is a significant amount of air trapped inside. Calling a professional is your best bet to solve the problem.

  6. Water leaks may not always mean it’s time for bleeding but do indicate issues with the radiator valves or connections.

An Allen key or flat head screwdriver can be used to bleed a radiator instead of a radiator bleed key.

You can bleed a radiator using a Allen key or flat head screwdriver instead of a radiator bleed key. The bleed nipple has a screwdriver and Allen key head slot.

Call Us For Help With Radiator Leaks

As the UK’s leading non-invasive central heating leak detection expert we specilise in identifying and fixing hidden heating leaks.

Our engineers use advanced techniques and tools including thermal imaging, acoustic listening devices and tracer gases. 

Our thorough approach and skilled team ensure quick, efficient repairs of radiator and heating leak problems, usually restoring your home’s warmth and comfort within a day.

ADI Leak Detection Customer Service Office Team

Adrian Morgan

Adrian Morgan CIPHE RP RHP is the founder & Managing Director of ADI Pro Leak Ltd. Adrian is also the Head Plumbing, Heating & Leak Detection engineer at ADI Leak Detection.

Adrian CIPHE RP RHP is proud to be registered with the Chartered Institute of Plumbing & Heating Engineering, a Registered Plumber and a Registered Heating Professional.