Airlock in radiator pipes

How to Clear Airlock in Radiator Pipes Without Using a Hose

Last updated on June 8th, 2024

An airlock in a radiator pipe can cause a radiator to not heat up or be cold at the bottom.

Airlocked radiators are annoying and will cause rooms to be cold.

I have been a full-time heating engineer for over a decade and have cleared many airlocks without ever using a hose or removing a radiator.

Do You Have Airlocked Radiators?

A radiator not working is an airlock symptom but an airlock is not the only possible cause.

Here are some other causes of a radiator that doesn’t work:

  • The radiator valve is turned off, blocked, stuck or broken
  • The thermostatic radiator valve is on the wrong side (only on certain old TRVs as new ones are bi-directional)
  • The radiator needs bleeding
  • The radiators need to be balanced
  • The radiator is not piped up correctly under the floor (only on a new radiator installation)
  • The designer radiator flow pipe is on the wrong side (certain new tall radiators have to have the flow pipe going into a specific side of the radiator)

How to Clear an Airlock in a Central Heating System

If you have recently drained the central heating system, it’s almost certainly an airlock causing the radiator to not heat up.

Here’s how I clear an airlock in a central heating system:

  1. Turn the heating on
  2. Close one valve (TRV or lockshield) on every radiator apart from the radiator(s) not getting hot
  3. Wait for the airlocked radiator(s) to get hot
  4. Bleed the radiator that is now hot
  5. Open every radiator valve

If you have more than one radiator airlocked and only one becomes hot after closing the valves, close a valve on the airlocked radiator that is now hot and wait for the other radiators to get hot.

How to Close Radiator Valves

You must turn off the radiators by closing either one of the valves.

Thermostatic Radiator Valves

Turn the head on the valve clockwise until it’s on zero or off.

Thermostatic radiator valve turned off
Thermostatic valve turned off

Lockshield Valves

Turn the lockshield radiator valve clockwise as far as it will turn.

You can turn some lockshield valves with your hand, but for some valves, you will need to remove the cap and turn the spindle.

To turn the spindle, you can use:

  • An adjustable spanner
  • Some water pump pliers
  • Or sometimes a hex key is needed
How to close different radiator valves

Radiator Still Not Heating Up?

If after closing all the valves on the hot radiators, the cold radiators are still not heating up, then it will not be an airlock causing the problem you have.

How to Remove Airlock From Gravity-fed System

Having air trapped in a gravity-fed central heating system can be a nightmare. An airlock in a gravity-fed system can cause the boiler to overheat and keep cutting out.

If you have problems with a radiator or two not heating up then you can follow the process above, but if the boiler is not firing up or cutting out, you will need to remove all the air.

Removing the air can take all day as hardly anything comes out, you have to just keep plodding on.

Here’s how I do it:

  • Turn the heating on
  • Bleed the radiators
  • Bleed the bleed valve (typically in the hot water cylinder cupboard)
  • Bleed the central heating pump
  • Repeat, repeat, repeat until the boiler stays fired up


You must turn off the valves on the hot radiators which forces the heat to the cold radiators, the full force of the central heating pump will go to where the airlock is.

This will force the air out of the radiator pipes and into the top of the radiator which can be bled out if needed.

I get airlocks regularly after draining and refilling central heating systems, and this method gets rid of the trapped air every single time.

If it doesn’t, then it won’t be an airlock problem you have.

Feel free to ask me any questions in the comment section below and I’ll try my best to help.

Please share this post if you find it helpful.


Will an airlock clear itself?

It’s possible over time for an airlock in a radiator pipe to clear itself but it’s not very likely.

What causes an airlock in a radiator?

Air trapped in a pipe causes an airlock in a radiator, typically after draining and refilling a central heating system.


  • Steven Reid

    I am a full-time plumber and Gas Safe registered engineer. I incorporated Housewarm Ltd. in 2011 to provide heating and plumbing services to homes in Newcastle upon Tyne, England. I now blog about what I've learned over the years to help DIYers and plumbers.

    View all posts
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7 thoughts on “How to Clear Airlock in Radiator Pipes Without Using a Hose”

  1. Hi Steven, followed you advice for clearing an air lock (combi boiler system) but no joy.
    Fitted 2 tall radiators in the summer, TRVs and lockstops fitted on same sides as the original rads – all was tested and was OK. Now the heating has been on for a week and was OK, but in last 48 hours the 2 new rads are now cold – the flow and return pipes are also cold. Any ideas other than a drain down and re-fill?

      1. borrowed an infrared thermometer and did just that – all the return pipes are about 15 degrees cooler than the flow now and all seems to be OK, thanks

  2. Thank you very much! This fixed my problem within minutes!

  3. Steve C

    Thank you! Your advice on how to clear an airlock worked first time, and so easy to do! Now we have a hot radiator in our cloakroom.

    1. Steven Reid

      Good to hear Steve, glad you got sorted and appreciate the feedback!
      It’s a great relief clearing an airlock, and it’s a lot easier if all the radiators have TRVs.

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