How To Bleed A Radiator? Is Your Radiator Hot And Cold?

If you have a radiator that feels hot at the bottom and cold at the top then you need to bleed your radiator. Bleeding your radiator is a very simple DIY task, but you will need a radiator key.

Bleeding A Radiator - Example
Bleeding A Radiator – Example

Once you have allowed the air to escape from your radiator the water will rise to the top of your radiator making the radiator energy-efficient and consistently hot all over.

Why Does Air Fill A Radiator

Over time air will begin to replace the water in your heating system, which in turn replaces water with air.

If your radiators need bleeding on the ground level then they will also need bleeding on all floors.

  • The system has been turned off over winter
  • New radiators always need bleeding
  • Old system or insufficient/older boiler
  • Your system might be leaking

Bleeding Radiators

When you bleed your system and replace the air with water you will need to top-up the system from the water-mains.

Bleeding a radiator
Bleeding a radiator

After each level of the house has been bled you must return to the boiler to turn on the overflow until the system pressure is stable for the boiler to kick-in.

If after bleeding you radiator it fills with air again and you cannot get the pressure back-up then your system leaks and you “MUST” call a plumber to investigate the system.

Do not do this if you do not have the correct tickets because a lot can go wrong and you will not be covered by your house insurance.

How To Bleed A Radiator?

Bleeding a radiator is a very simple job, but you need the right tools.

Do not use a pair of plyers because if you cannot turn the radiator valve to the off position it will flood the room until your central heating system has emptied.

The correct tool for bleeding a radiator is a “radiator key” this key will fit snuggly onto the valve and will open up the valve so the air can escape.

As the air releases the water can rise to the top making your system more productive with more heat emitting from your radiators.

Radiator Key Examples
Radiator Key Examples

Step-by-Step Guide

Here are the steps needed to bleed a radiator and make it more energy-efficient. The more water you have in your radiator the hotter it will become.

After the summer months when radiators are not used they will become full of air, so once a year you must keep on top of your radiators.

Start at the top of the house and check the overall pressure after you bleed each radiator. If there is not enough water in the system then the pressure will drop and you should top up the water pressure by a switch or a filling loop.

  1. Grab a radiator key, towel or bowl in case of leaks
  2. Push the key into the TOP valve
  3. Turn left NOT right, lefty loosey and righty tightie
  4. You will hear a hissing sound, this is the air escaping
  5. As soon as you hear water spitting out turn the radiator off (right)
  6. Your radiator is not full of water for maximum heat!
  7. Check the overall boiler pressure, located behind the front panel
  8. If the pressure has dropped just top-tup the system
  9. You have successfully bled a radiator
  10. Now continue doing this until all radiators have been bled


Bleeding your heating system is a DIY task most homeowners should accomplish.

You should be bleeding your system each year so you get the maximum heat from your radiators.

Happy Heating 😉

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