How to bleed a radiator
Does the top section of your radiator feel cool to the touch, while the bottom of it is nice and warm?
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.
Summary: How to Bleed a Radiator in 10 Easy Steps
- Turn on the central heating
- Feel all the radiators in your home
- Switch off the heating
- Wait for the radiators to cool completely
- Grab your supplies
- Find the bleed valve
- Loosen the bleed screw
- Wait for the hissing to stop completely
- Re-tighten the valve and clean up the drips
- Turn on the heating again
1 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.
2 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.
3 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 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.
5 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.
6 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 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.
8 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 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 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.