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How to bleed a radiator

How to bleed a radiator

With temperatures finally slumping in Sidcup, chances are you’ve fired up your central heating again recently, maybe for the first time since the start of this year’s glorious long summer.

If your radiators seem like they’re not heating up like they should, and you’re concerned about an expensive repair bill – don’t worry. Chances are your radiators just need ‘bleeding’.

A common cause of a radiator running inefficiently is a build-up of trapped air inside, hindering the flow of hot water through it.

Cold spots on the surface, or the radiator taking longer than normal to warm up, are common signs that the radiator has air trapped inside. Letting that trapped air escape by ‘bleeding’ your radiator will get your radiator working like new again.

It’s a simple treatment that isn’t as gruesome as it sounds and can easily be done by a layperson. All you’ll need is a radiator key, a rag or cloth to catch any drips, and a bit of confidence.

Here’s our quick guide on how to bleed a radiator…


Step 1 – turn your central heating off

This is important! Before you do anything else, turn your central heating off and let your radiator cool down completely. (If you don’t, you’ll likely end up with hot water all over your floor!)

Step 2 – let the air out

This is the actual ‘bleeding’ bit of the process. Fit your radiator key into the radiator’s valve. (If you’re struggling to find the valve, it’s usually on the top of the radiator). Open the valve gently by turning the key – normally anti-clockwise – until you hear a hissing sound. That’s the trapped air escaping.

Ensure you’ve got your rag or cloth to hand to catch any little drips of water that escape during the bleeding process.

Once the hissing stops, close the valve again. Be sure to do this quickly, as there’ll be water on the way once the trapped air has been let out.

Step 3 – turn your heating back on and check your pressure

Once the valve is back in its original position, you can turn your central heating back on again. Last thing before you’re done is to check your boiler’s pressure gauge. Sometimes the system pressure drops as a result of bleeding a radiator, and may need topping up. (Check your boiler’s instruction manual if you’re not sure how to do that).


If your radiators are giving you grief - or if you have any other issues related to your plumbing, heating, drains or electrical systems - get in touch with XP Plumbing and Heating.

From our base in Sidcup, our qualified plumbers, heating engineers, electricians and more have great coverage throughout the local area - including Eltham, Bexleyheath, Bromley, Chislehurst and Greenwich - and further afield, into the rest of London and north Kent.

Get in touch with XP Plumbing and Heating today.