Towel Radiator

A Complete (DIY) Guide to Bleed a Radiator

If the radiators in your home have cold spots at the top or aren’t heating up as they should, air may be trapped in them.

This means you need to release the trapped air – a process known as bleeding your radiators – to make them work again.

Bleeding your radiators helps you heat your home effectively and efficiently, reducing your energy bills and is surprisingly easy if you know what you’re doing.

If you can hear pipes banging or radiators gurgling in your home, this is usually a sign that there is air trapped in your radiators, and you should bleed them. Fortunately, bleeding your radiators is simple and easy to do, so follow our guide on how to bleed a radiator yourself, and you’ll be saving money with more efficient heating in no time!


How To Bleed a Radiator

Follow our simple step-by-step guide to check and bleed your radiators safely:

1. Turn your heating on

Firstly, turn on the heating in all the rooms of your house (or flat) and wait for your radiators to warm up. Depending on the number of radiators in your home, this may take some time, so get comfy.

2. Find the radiator(s) that need bleeding

When your heating is on, you should carefully check each radiator to see if it has an even temperature across the whole radiator. If you find any radiators with cold spots near the top or hear strange noises, there’s a good chance of trapped air in your heating system.

3. Turn off your heating

Now you’ve found the problem radiator(s), you want to turn off your heating so the radiators won’t burn you when you bleed the system.

4. Place a towel or cloth beneath the radiator bleed valves

Find the bleed valve on your radiators and place an old towel or cloth beneath it to catch any water that may leak out during the bleeding process. Most bleed valves look like a round hole with a square inside and are fitted on the top corner of a radiator.

5. Open the bleed valve

Using a radiator key, open the bleed valve on your radiator. There should be a hissing sound as air escapes your heating system, but the valve could be blocked if no water or air comes out.

NOTE: If you don’t have a radiator key, don’t worry – we’ll explain how to open a bleed valve without a key in the next section.

5a. Unblock the bleed valve

If the bleed valve is blocked, close the inlet and outlet valve at each end of the radiator and remove the screw from the centre of the bleed valve.

6. Close the bleed valve

Once the open bleed valve stops hissing and water begins to leak out, turn the key clockwise to close the valve again.

7. Check the boiler pressure

Repeat steps 4-6 for each radiator that needs bleeding, then check the pressure of your boiler’s water pressure gauge. If the pressure is normal (1-2 bars), you can switch your heating back on as normal. However, if the pressure is too low (below 1 bar), you’ll need to repressurise the system.


How To Bleed a Radiator Without a Key

While it’s always best to have the right tool for the job, it’s quite easy to lose a radiator key and be left without an obvious way to bleed your radiators. Fortunately, you don’t have to sit in the cold until you can order a replacement, as you can also open the bleed valve on your radiator using other common tools such as:

Flat head screwdriver

Some radiators feature bleed plugs with small slits in the middle, so you may be able to open the bleed valve using a flat-headed screwdriver. Just insert your screwdriver neatly into the slot and turn counterclockwise (left) to open the valve, like you would with a valve key.

Allen key

Many bleed valves use square plugs, so you may be able to open them with an Allen key if you can find one in a matching size. Who knows, the Allen key you got with that flatpack furniture might come in handy again, so check if you have a compatible key if you’ve lost the valve key for your radiator.

Adjustable wrench

This last one is a bit of a long shot, as most valve plugs are recessed into the radiator, but you may be able to grab the plug with the teeth of an adjustable wrench.


Do You Bleed a Radiator When It Is On or Off?

You should never bleed a radiator when it is on, as the water may be dangerously hot and spray out of the bleed valve when opened. Always wait until your radiator is cool enough to touch before attempting to bleed it, as you may suffer burns when it is on.


Why Is My Radiator Still Cold After Bleeding?

Bleeding a radiator is one of the first things people do when trying to fix a faulty radiator and is usually enough to resolve the issue, but what if your radiator is still cold after bleeding? If you’ve followed our instructions on bleeding a radiator and are still out in the cold, try these other fixes:


Check your Thermostatic Radiator Valve (TRV)

A common problem that will stop your radiator from getting hot – even after bleeding – is a stuck pin on your Thermostatic Radiator Valve (TRV). The TRV is the larger of the two radiator valves with temperature control numbers, and you should be able to see the TRV pin by removing the cap or head of the TRV valve.

TRV pins can easily get stuck in the shut position preventing water from flowing into your radiator, so try to gently loosen it with an adjustable spanner or set of grips to fix a stuck pin. After releasing the TRV valve, turn your heating back on to test whether your radiator is working.

Flush your radiator to get rid of an airlock
If your radiator still isn’t working after fixing a stuck TRV pin, there may be an airlock in your system preventing water from flowing evenly around your heating system. Unless you have plumbing experience, we don’t recommend flushing your radiator, as it is an involving process that requires you to:

  • Shut the TRV and lockshield valve
  • Open the bleed valve with a towel to catch any spills
  • Remove the whole air bleed assembly
  • Add a ½ inch male connection to connect a garden hose
  • Turn your heating system off
  • Feed the hose outside or into a large container
  • Open the TRV
  • A large amount of water will flow out of the radiator through the hose
  • This will hopefully remove the airlock and allow your radiator to work again

Balance your heating system

If you’ve done all of that and your radiator is still cold, it may be due to an uneven flow of water around your system. In this case, you will need to have your heating system rebalanced which is a complicated process that is best left to the professionals.

Replace your Thermostatic Radiator Valve (TRV)

TRV pins will often get stuck in the shut position, but they are far from the only thing that can malfunction in a thermostatic radiator valve, as TRVs tend to degrade over time. Fortunately, replacing the TRV can fix the issue of your radiators staying cold, give a new lease of life to older radiators and even liven up your room if you opt for a decorative TRV.


How Do You Bleed a Towel Radiator?