bleeding a radiator

Action: Bleed your radiators to make your heating more efficient

The simple, easy and free check on your heating system can save energy, carbon emissions and money!

Most modern central heating systems use a boiler of some sort – gas, electric, oil or whatever – to heat water that is pumped around a number of radiators around the house – typically one in each room. The hot water heats up the radiators which then “radiate” that energy into the room.

However, if there is air in a radiator it is far less efficient, and also may be prone to internal corrosion. The process of removing air from your heating system is called “bleeding” and is very easy to do. You should bleed your radiators when you start up your heating system each year, and check them regularly throughout the cold weather.

Why is this important?

If we are to manage climate change and global warming, every household heating system needs to be as efficient as possible. Running an inefficient system means you burn more fuel, which costs money and also increases your carbon dioxide emissions. Bleeding your radiators will:

  • save you money on your fuel bills
  • reduce the amount of carbon dioxide emitted by your household
  • reduce your consumption of fossil fuels (most boilers run on natural gas)
  • extend the life of your heating system
  • of course, your house will be warmer too!

What to do

radiator key

Please take advice from a plumber or heating engineer if you are not familiar with your heating boiler or confident about this task. Water in a central heating system is extremely hot and under pressure.

  • Firstly, turn on your central heating and open the radiator valves to full power. These are the (usually) white knobs you find at the top or bottom corner of your radiator
  • When the heating has been on a while, carefully check how hot each radiator is
  • If the system is circulating hot water correctly but the radiator is cold, or is cold at the top, air is in the system and it’ll need bleeding
  • You’ll need a radiator key to bleed your radiator (pictured)
  • Some radiators can be bled using a standard screwdriver and/or are designed to make collecting any water that escapes as easy as possible
  • As well as the key or screwdriver you will need a bowl to catch water and a couple of dry tea towels
  • Turn your central heating off and let the radiator cool down before beginning (to avoid scalding)
  • Find the square bleed screw at the top corner of your radiator
  • Place the bowl or tray directly underneath it at the base of the radiator
  • Place the radiator key over the bleed screw, cover it with another cloth and slowly turn the key anti-clockwise for about half a turn.
  • As the air is released you’ll hear a hissing sound; hold the cloth close to prevent water dripping or spitting
  • Once air stops hissing and water begins to trickle out steadily, tighten the screw again
  • Be careful not to over-tighten and damage the valve
  • Wipe down the radiator to avoid leaving any moisture which could cause rust or staining
  • Switch the heating on again, and check the boiler pressure
  • If there was a lot of air to release you will need to top up the water pressure by using the filling loop on your boiler
  • This is usually a tap or lever on the main water supply to your boiler
  • Take care not to overpressurise the system; there should be a clear pressure gauge
  • If you have any doubts at all, take advice from a plumber or heating engineer.

Finally, check again that all the radiators are heating evenly and that none of the bleed valves are leaking. You may need to bleed some radiators a second time as air shifts around the system, but if the problem still isn’t resolved, contact a heating engineer.

Take action

Take this simple action as soon as you start using your heating system this year and then regularly; save money, warm your home more effectively, and reduce your carbon footprint. It’s easy and really does make a difference.

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