How To Bleed A Radiator – Safely

When you notice that one or more of your central heating radiators doesn’t seem to be getting as warm as it used to, then it’s time to do a bit of simple home maintenance to fix the problem.

There are some jobs that you don’t need to call in the experts to do, bleeding air from radiators is one of those jobs, just follow our simple step by step guide on how to bleed a radiator – safely.

All you need is a radiator key, a cloth, and a small container to catch any drops of water. It really is a simple job to do and best of all, doing it yourself will save you money.

You’ll soon have those radiators working more efficiently and back to producing their full heat output. Just follow the step-by-step instructions in the table below.

8 Easy Steps: How To Remove Air From Your Radiators

StepWhat To Do
1Turn on the central heating system
2Identify any cold spots by feeling all the radiators
3Turn off the central heating to allow the radiators to cool down
4Gather together the radiator key, a cloth and a small container
5Slowly loosen (turn anti-clockwise) the radiator bleed valve using the radiator key
6Wait for the hissing noise to stop
7Re-tighten (turn clockwise) the radiator bleed valve using the radiator key
8Turn on the central heating system

Step 1 – Turn On The Central Heating

The first thing you need to do is to turn on the central heating system, either by turning up the room thermostat or adjusting the time control clock so that the boiler will start up.

Make sure that all the radiators are turned up fully. You might need to turn up any thermostatic valves if you have them fitted (the chunky thing with numbers on, fitted at the top or bottom of each radiator that regulates the heat of the radiator). Then it’s just a case of waiting for the radiators to get hot.

Step 2 – Identify Any Cold Spots

When the radiators are nice and warm, this is the time to check each radiator for any cold spots, starting at the bottom of the radiator working your way up to the middle, and then to the top. Remember that the majority of the radiators will be hot to the touch, so be careful when checking them for cold spots.

You might also notice that a particular radiator takes a long time to heat up, or makes a gurgling noise. You might even find a completely cold radiator that is totally air-locked.

Step 3 – Turn off the central heating

Turn off the central heating and allow the radiators to cool down. It’s important that you let the radiators cool down as you don’t want any hot water spurting out when you are bleeding the air out.

When you think the radiators have cooled down, just give them a feel and if they are cool to the touch then you are ready to carry on to the next step.

Step 4 – Get Organised

Gather together the equipment you’ll need to bleed the radiators:

  • The radiator key – This is that strange-looking small key, with the end that looks like it fits onto a square, you know the one, it’ll be in the draw with all the other important bits and pieces that you need to keep safe. If you have lost the radiator key, not to worry, as they can easily be bought from DIY stores.
  • A cloth or towel – This is for catching any drips of water that might come out of the radiator when the bleed valve is opened. You probably notice that the water that comes out of the radiator is very dirty. So don’t use your best cloths or towels for this job.
  • A small container – It’s always a good idea to place a small container below the radiator where you are working as the water can sometimes run down the back of the radiator and drip onto the floor or carpet and cause a stain.

Step 5 – Slowly Loosen The Radiator Bleed Screw

If you found that most of your radiators need bleeding then start with the ground floor radiators, beginning with the ones furthest away from the boiler.

The next step is to slowly loosen (that’s turning anticlockwise) the radiator bleed valve, that’s the little recessed valve at the top of the radiator at one end, it looks like a small square shaped bit of metal.

Make sure you don’t undo it too much as you don’t want the screw to come out completely.

What you’ll notice is that if there is any air trapped in that radiator, a hissing noise will begin, this is all that trapped air getting pushed out of the radiator by the water inside the radiator.

Step 6 – Hissing Noised Has Stopped

At this point, when the hissing or gurgling noise has stopped. In some cases, this can take up to 30 seconds or more especially if there is a lot of air trapped in the radiator or if it’s a particularly big radiator.

Once you notice that there is a nice steady flow of water coming out of the bleed valve then you can be pretty sure that you have released all the air trapped in that radiator.

Step 7 – Tighten Up The Bleed Valve

Re-tighten the bleed valve (that’s turning it clockwise) using the radiator key. Don’t be tempted to overtighten the bleed valve as it can easily be damaged if too much pressure is applied.

Use your cloth to dry any areas where the water has come out of the radiator and empty your container if any has collected in it.

Step 8 – Turn The Heating On

Turn on a central heating system, check that there are no drips of water from the bleed valves, if there are any drips just give the bleed valve a bit more of a tighten with the radiator key.

Well Done – Job Complete

Well done you have successfully bled all the air that was trapped in your radiators, we knew you could do it, now all that’s left for you to do is, relax.



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