How to bleed a radiator

The Quick 10 Step Radiator Bleeding Guide


Confident you can get the job done yourself? Simply follow this quick 10 step radiator bleed guide!

  1. Turn your heating on.
  2. Feel the top of every radiator (don’t burn yourself) and check for cold spots
  3. Turn off your heating and wait till your rads are cool.
  4. Grab your bleed key and old cloth for catching drips.
  5. Insert your bleed key into the radiator bleed valve, holding your cloth underneath.
  6. Carefully turn anti-clockwise to open the valve and listen for hissing as the air escapes.
  7. When water comes out, turn the key back clockwise to close the valve.
  8. Repeat on all radiators with cold spots.
  9. Check boiler pressure and rebalance & repressurise if necessary.
  10. Kick back, relax and get cosy.

Radiator Bleeding Video Guide


If you require a little extra help and support, here’s a handy video to help you get the job done.

Why Should I Bleed My Radiators?


Bleeding your radiators will help to remove any excess air that may have become trapped in your radiators.

This trapped air can cause cold spots on the surface of the radiator, reducing its efficiency and effectiveness when heating your home.

Your radiators work alongside your boiler and if they are not working properly you’ll be paying for your energy without actually feeling the benefits!

Bleeding a radiator is a simple job – and one that you can do yourself – leading to a warmer home and cheaper energy bills!

Please Note: If you find you still experience cold spots after bleeding your radiators, this may mean that you have a build up of rust or ‘sludge’ in your central heating system and you should contact a qualified engineer.

What ‘Tools’ Do I Need To Bleed A Radiator?

  • Radiator Bleed Key/Flat-head Screwdriver
  • Cloth or towel to catch drips
  • A container to catch water (optional)

How To Bleed A Radiator For Energy Efficiency


Step 1 – Turn Your Heating On


First up, turn the heating on so that all of the radiators heat up.

A man turning a thermostat on

Wait until the system gets up to temperature, before moving on to step two.

Step 2 – Find Out Which Radiators Need Bleeding


Once your heating is up to speed, go and check every radiator to see which are heating up properly and which are not.

A hand checking the level of heat at the top of a radiator

BE CAREFUL! Radiators can get really hot and you don’t want an unexpected trip to A&E to deal with!

Cool spots – especially near to the top of the radiator – mean that there could be air trapped inside and you’ll need to bleed that radiator.

a graphic that shows a radiator that is cold at the top and warm at the bottom

Once you’ve found which radiators have cold spots, it’s time to bleed them.

Step 3 – Bleed The Radiators


Switch off your central heating and give the system time to cool down – this will allow you to handle the radiators without scalding yourself.

At the top of the radiator, you’ll find a bleed valve – or nipple – at one end (like in the image below).

a radiator key being placed into a radiator bleed valve

Insert the radiator bleed key into the groove of the bleed valve and carefully turn it anti-clockwise (you may be able to use a flat-head screwdriver here).

You should hear a hissing sound as the air escapes from the radiator.

Hold the bleed key in position until water begins to dribble from the radiator bleed valve.

water starting to bubble from the bleed nipple on a radiator

With more modern bleed valves, you may find that water emerges as a ‘jet’ of water, so you’ll need to be on your toes and close the valve quickly should this start to happen.

Be careful NOT to over-tighten the radiator bleed valve as you close it, or you may cause damage.

Step 4 – Check The Pressure Of Your Heating System


Once you’ve closed the radiator bleed valve, go and take a look at the pressure gauge on your boiler (you could get someone else to do this if you need to).

Boiler pressure gauge at 1 bar

If the pressure is too low, you will have to use the ‘filling loop‘ to top up the level of water in your central heating system – tips on how to do this are below.

Once you have done that, turn your heating back on and repeat the same checks as above.

You may find that you have to bleed your radiator(s) and re-pressurise your system a couple of times to get the job done.

Please Note – ALWAYS turn OFF the power to your boiler when re-pressurizing your central heating system.

How To Re-Pressurise Your Heating


To re-pressurise your central heating, you’ll need to locate your filling loop.

The filling loop is the pipe that connects your central heating system to the mains water supply – some systems have an external one, while others have an internal loop.

The filling loop isn’t part of your boiler – but it will connect to it, so should be nearby.

If you have an external filling loop, it will probably look something like the image below and you’ll have to turn the taps to allow water into the system.

Image of an external central heating filling loop

The taps you are looking for are normally black in colour and may even have the words ‘filling loop’ on them.

Don’t turn any taps other than those connected to the filling loop.

Turn the taps slowly in order to safely control the flow of water into the system, being careful not to exceed the required level.

You should hear water being fed through the inlet pipe and into your central heating system.

Alternatively, you might have an internal filling loop key attached to a panel at the bottom of your boiler – like the one in this video – or a couple of filling taps situated underneath, like this.

Internal filling loop taps for a central heating boiler

Please Note – Different boiler manufacturers and installers will recommend different optimum operating pressures for your boiler and central heating, so be sure to consult your user manual. If you are unsure of what the correct pressures are, please seek professional advice.

You’ve Just Bled Your Radiator!


Well done – if you followed all the steps above, you should have successfully bled your first radiator.

If the problem persists, simply repeat the process and you should be fine.

It could be that you didn’t get all of the air the first time you did it and it’s not uncommon to have to bleed a radiator a few times to get all of the air out.

Good luck and happy radiator bleeding!


stay safe and happy heating

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