How to bleed a radiator & fix your heating problems in 10 easy steps

Does the top section of your radiator feel cool to the touch, while the bottom of it is nice and warm? The dreaded cold spots mean there’s air trapped inside that has risen to the top, taking the place of the hot water that should be there to heat the radiator.

Luckily, letting the air out (or bleeding) the radiator is a really simple job that will not only help keep your home feeling toasty, but could save you money on your bills. That’s because your radiators work alongside your boiler, meaning you’re paying for the same amount of energy, without feeling the benefit of all that lovely heat. And by making your home more energy-efficient, you’ll be doing your bit for the environment too.

Here’s everything you need to get rid of the cold spots in 10 easy steps.

1. Turn on the central heating

Switch on the central heating and make sure your radiators are turned up fully (if you’re not sure how to do this, see our troubleshooting guide below). Wait until all the radiators in your home have heated up before moving on to step two.
Someone adjusting the valve on a radiator

2. Feel all the radiators in your home

Single out the radiators that need bleeding by touching them all over for cold spots. It’s a good idea to wear gloves at this point, so you don’t burn yourself.

Tell-tale signs that your radiators need bleeding include gurgling noises, a radiator that takes a long time to heat up, or the top section feeling significantly colder than the bottom. In really severe cases the radiator may even feel completely cold.

Check all the radiators in your home at the same time, as you may find you need to bleed more than one. If this is the case, bleed the radiators on the ground floor first, starting with the one that’s furthest away from the boiler, before moving on to the upper floors of your home.
Hand checking the temperature of a radiator

3. Switch off the heating

Keep your radiator intake valves open, but make sure you turn off your heating before attempting to bleed your radiators. Some water pumps will actually suck more air into the heating system if they’re turned on when you open up the bleed valve.

4. Wait for the radiators to cool

Feel all over your radiators for heat and don’t attempt to bleed them if they’re still warm.

You don’t want boiling water to spurt out when you open the valve, for starters. But secondly, it’s good to let your radiator's contents settle completely before you start, to make your bleeding really effective.
Radiator valve being opened

5. Grab your supplies

You’ll need a radiator key, a cloth to hold, old towels to put down and a container to catch any drips.

Bleed valve keys are supplied with the radiator, but if a search of the bits and bobs drawer has proved fruitless, you can buy one at a DIY shop.

Some modern radiators have a new style of valve that can be turned with a flathead screwdriver. However a normal radiator key will also work, and has the added benefit of giving you more control over how you open and close the valve.

Sometimes, the water that comes out of an old radiator can be discoloured, so putting down old towels is a must if you have light coloured carpets.
Radiator bleed valve key

6. Find the bleed valve

The bleed valve will be at the top of the radiator on one of its ends (it looks like a round hole with a square inside it). This is where you’ll be releasing all that air and water, so put your old towels down on the floor underneath it, with the container on top of them to catch any spillages.

7. Loosen the bleed screw

Attach the radiator key to the square bit in the centre of the bleed valve or, if you’re using a flathead screwdriver, put the blade into the groove.

Turn the bleed screw anti-clockwise. The cloth will help you get a good grip, and is handy for catching any drips at this point. Just one quarter to a half turn is enough - never open the valve fully or water will pour out once the air is released. You should hear a hissing sound as the air escapes.
Bleed screw on a radiator being loosened with a screwdriver

8. Wait for the hissing to stop

Once all the air has been released, the valve will start to trickle water which can be mopped up by the cloth you’re holding underneath. With modern, screwdriver operated valves, the water tends to come out in a small jet, rather than a dribble, so don’t be alarmed.

Wait for a steady stream of water (not just a sputtering mix of air and liquid) to appear. This is the sign you’re looking for that all the air has gone.

How long should it take to fully bleed a radiator? That can vary, depending on the amount of air that’s trapped inside and on the size of your radiator. Sometimes it can take 20 to 30 seconds for a radiator to bleed, but it might even take a full minute for larger radiators.

9. Re-tighten the valve

Using the radiator key or screwdriver, re-tighten the bleed screw in a clockwise direction. Don’t be tempted to do it up too tightly, as this could damage the valve.

Using a towel, wipe down any water which may have spilled onto the radiator or its pipework to avoid any future rusting. Then move on to the next radiator in your home.

10. Turn on the heating again

Once all your radiators have been bled, you can turn on the heating again to check your work’s been successful. Make sure all the radiator panels feel hot all over and that there are no leaks or drips from the bleed valve. You may need to bleed some radiators a second time.

You’ll also need to check the boiler is still showing its recommended heating pressure level (normally 12 to 15 psi). By releasing excess air from the radiators, you’ll have lowered the overall pressure of your heating system. If the pressure’s fallen too low, heat may not be able to reach some of the radiators on the upper floors of your home.

If this is the case, top up the pressure by using the filling loop on your boiler. It looks like either a tap or a lever on the main water supply to your boiler.
Hand adjusting the settings on a combi boiler

How do I turn on my radiators?

To check if a radiator needs bleeding, you’ll need to turn it on fully. You’ll also need to keep its intake valves open while you’re letting the air out. Luckily, with today’s modern thermostatic valves, it’s easy to see when a radiator is turned up to the maximum. However, with older-style wheel head or lock shield valves, it isn’t quite so obvious. Just remember you need to turn them fully, in an anti-clockwise direction. If your lock shield valve has lost its plastic adjuster, a spanner will also do the job.

All the radiators on the top floor of my house feel cold. What should I do?

Your heating system may not have a high enough pressure to pipe hot water to the top floors of your house. Check your boiler to see if it needs topping up.

What if my radiator feels hot at the top, but cold at the bottom?

This is normally caused by a build-up of sludge - a mix of dirt from water and rust - which settles at the bottom, restricting the flow of hot water and leaving some areas of your radiator panel feeling cold. If your heating system is more than 10 years old, you’ll almost certainly have some corrosion. To fix the problem, you could take the radiator off the wall, take it outside and flush it through with a hosepipe. If that sounds too much like hard, dirty work, call in a heating engineer, who can professionally (and cleanly!) power-wash the whole system.

How can I stop my radiators hissing and banging?

Noisy pipes and radiators could be caused by lime scale building up in the heating system - and it’s a common problem in hard water areas. You’ll need to call a heating engineer to clean it out, and they can also fit a hard water filter to stop it from happening again.

How to bleed a radiator without a key?

Pliers may work, but there’s always a chance you could damage the valve, so a proper radiator bleed valve key is best.

I’ve bled my radiators but they’re still not heating up. What should I do?

Before you call out a heating engineer, there are some easy checks you can make. Some radiators may just need to be bled a second time. If all the radiators in your home (or just the ones on the upper floors) aren’t heating up, it could be that the boiler pressure has got too low and needs to be topped up, using the filling loop on your boiler. Another simple thing to try is switching the electrical supply to your boiler off and then on again. This will reset the boiler and may solve the problem.