Bleeding radiators

If your radiators are noisy or cold at the bottom, the easiest fix and first port of call will be to bleed them. This is a relatively easy job that most people will be able to learn quickly. It is definitely very useful a skill to have.

Bleeding Radiators for effective Central Heating
Bleeding Radiators can make your Central Heating more efficient



Things you’ll need

Radiator bleeding key
Bucket or bowl


What to do


Assess the problem


  1. Start with the central heating off.
  2. You need to to make sure that the radiators can be fixed by bleeding them.
  3. Fully open all of the valves on the radiators – these are the thermostatic radiator valves, including the valves on any heated towel rails (not the bleeding valves) – and then turn the central heating on. This will tell you how your system is working overall.
  4. If some of your radiators are hotter than others, after you’ve finished bleeding radiators you will want to take the job one step further and look at balancing the radiator system throughout the home, this is a more complex  job; one you may wish to ask your local Stopcocks Woman Plumber or another trusted professional to carry out for you. However, if there is simply a knocking noise in them bleeding the radiators will help to sort the issue.
  5. You are removing air from the system. It has been filling a space that may have been caused by water leaking out, so check thoroughly for leaks, which could be in the pipework or from valves and radiators.
  6. Bleeding radiators frequently causes the pressure in the system to drop, so it’s likely the problem will return. Topping up the pressure in your boiler correctly can be a job that requires a considerably higher level of skill, something else you might wish to call your local Stopcocks Woman Plumber to do.
  7. If all this feels too much, just call 0800 8620010 to take advantage of our Special Offer throughout March and book a Plumbing Health Check for just £60 click here

Bleeding the radiators


  1. Locate the bleeding valve, which is normally situated in the top of the radiator either at the end or sometimes on the back and place the key inside, turning it anti-clockwise. You will hear a hiss of air when you turn the key – this is the excess air escaping. Allow it to slowly escape the radiator by not opening the valve too much.
  2. Keep your hand on the key at all times and wait until water starts to drip out, wiping it away with your cloth. As soon as the hiss of air stops and the water starts to flow a little steadier, close the valve again.
  3. Complete these steps again on each radiator in your system, but take care. Air might not be present in all radiators, and if water is the first thing that comes out, make sure to close the valve straight away.
  4. If you have a combi boiler or a sealed system check the pressure and top up to 1 bar. If you do bot have this type of system you will not need to worry about pressure.
  5. Once everything is done, turn on the central heating again and wait for everything to heat up. Ensure that none of the water is dripping out of the valves and check that all of the radiators are heating nice and evenly.

Safety tips


Always ensure the central heating is off and that you allow sufficient time for it to cool before you attempt bleeding radiators. Failure to do this might see hot water escaping and causing burns if care is not taken.

Please note that this advice have been written strictly for reference only. Stopcocks Women Plumbers do not accept any liability for any damage caused to an individual, property or anything else as a result of following this advice. If in doubt call 0800 8620010

Bleeding radiators
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