How to bleed a radiator in 7 easy steps
By Matt Mostyn Monday 30 November 2020
If you can hear pipes banging or radiators gurgling, it's usually a sign that it’s time to bleed your radiator. And even if you don't, it's still good to do at least once every year. So here it is, our easy step-by-step guide to bleeding radiators, without causing you to swear!
We’ll show you how to check if trapped air is the problem, and how to take the right steps to fix it. We’ll also give you ideas about what else might be making your radiator cold.
So why bleed a radiator?
Quite simply, trapped air stops warm water circulating around your radiator. It’s what makes the radiator cold at the top, but warm at the bottom. That’s because the air rises to the top, forming a pocket and blocking the flow.
By the way, if your boiler has actually stopped working altogether, and you’re without hot water or heating, check out our guides to how to reset your boiler, what to do if your boiler loses pressure, what to do in a power cut, costs for repairing or replacing your boiler, how to defrost a frozen condensate pipe, and other common boiler problems.
How to check if your radiator needs bleeding
There are a couple of different reasons why your radiator needs to be bled. Here’s how to check the culprit. With the heating turned on, feel along the top of the radiator. If it’s cold at the top and hot at the bottom, it’s likely a build-up of air in the system.
If, on the other hand, your radiator’s hot at the top but cold at the bottom, or if it has cold patches, you could have a build-up of sludge. And that means bleeding it may not fix the problem. More on that below.
Either way, it’s a good idea to bleed your radiators once a year – even if they seem to be working properly. The ideal time is when you turn the central heating back on after the summer. And then check them once in a while to make sure they’re staying hot.
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How to bleed a radiator: our step-by-step guide
What you need to begin
Before you begin, gather the following:
A radiator key – you can get one from most DIY stores
A cloth or rag to catch any drips
A towel to protect your carpet from dirty water
Some more modern radiators can be bled without a key. But if yours can’t be, we recommend the key option, or a screwdriver as an alternative. Take a look at the radiator’s bleed valve, which has a square screw or bolt. You’ll find it at the top of the radiator, either on the side or at the back. If there’s a small slit in the middle, you could use a flathead screwdriver to open it.
Only use a flathead, not a cross-head screwdriver – which can damage the valve. And definitely don’t use pliers, for the same reason.
7 easy steps to bleed a radiator
Start by turning the heating off, and most importantly, wait for the system to cool down, so you won’t burn yourself if water escapes.
Find the bleed valve.
Put your cloth under the valve, ready to catch any water that escapes.
Fit the radiator bleed key (or your flat head screwdriver, if that works) in the screw and turn it anti-clockwise about a quarter of a turn, or until you hear a hissing noise (that’s the air coming out). You might also get a few drops of water, so have cloth at hand!
Wait until all the air has escaped. When that happens, water will start seeping out instead.
Next, tighten the valve again. It needs to be tight enough to stop air getting in, but not so tight that you can’t open it the next time.
Turn the heating back on and your radiator should soon be toasty all over!
Top tip: valve fall-out
When you’re bleeding your radiator, don’t turn the screw on the bleed valve more than one-and-a-half turns, or it could come out completely. If that happens and you can’t get it back in right away, don’t panic. Turn the radiator valves off via the screw or dial valve at the bottom, and that should stop more water getting in while you re-attach the screw.
Bleeding a radiator with a combi boiler/pressurised system
For combi boilers, and boilers/ systems that are pressurised, there’s one extra step. After you’ve released the air, check the pressure gauge on the front of your boiler. It should usually be between 1 and 1.5 bars – but check your boiler manual to find out for sure.
With these boilers, you can actually let out too much air, making the pressure too low. If that happens, it’s usually just a question of turning a valve to let in some more water – but again, check your boiler manual to find out the process for your model.
Top tip: can’t find the boiler manual!
To be honest, who can, right? Instead, check the make and model on your boiler itself, then just hop online to their website to download a new one.
Decisions, decisions? Book a free appointment with one of our trained engineers to find out which boiler will work best for you.
Top tips for the warming of bits
Want to perfect your yearly radiator ritual? Here are our other best bits of advice for success:
The best time of year to bleed a radiator
It’s a great idea to make radiator bleeding a yearly habit – so perhaps do it at the beginning of the heating season (around late September/early October), before you really need it. That way, both your boiler and your heating system will be running at their best by the time you really need them.
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How to keep your heating costs down
Experts recommend not having your radiator on too high. Instead, here’s a quick rundown of the perfect temperatures to aim for, room-by-room:
Hallways, corridors, kitchens, and storage rooms are often just right at around 16 to 18°C.
You’ll actually sleep better in a bedroom that’s cooler rather than warmer. 18 to 19°C is ideal – and perhaps even a degree or 2 less than that.
Living rooms usually feel perfectly warm at around 19-20°C.
Bathrooms and children’s rooms are often better set slightly higher, between 18 and 24°C – depending on what feels comfy for you.
So keep an eye on your radiator dial or thermostat and adjust to suit.
What to do if your radiator still isn’t getting hot
If your radiator still isn’t getting hot, even after bleeding, you probably need to call a heating engineer. And if the bottom stays cold, it could mean a build-up of sludge. In which case, your system will need a Powerflush. The older your system, the more likely you’ll need one. Get a Gas-Safe-registered engineer to have a look. If needed, they’ll connect a machine to your system to flush it out.
Which radiators to bleed first
If your home has more than 2 levels, start by bleeding the ones located closest to your boiler first.
How long should it take to bleed a radiator?
The average radiator should take no more than 20 to 30 seconds to bleed – though it can vary depending on the radiator size, and the amount of air trapped inside. As a rule, keep bleeding air until the hissing noise stops and water starts trickling out.
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