How to Bleed a Radiator

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There are some jobs that should be left to the experts and then there are others that you can quite easily get done yourself.


Keeping your home’s heating system and radiators in tip-top operating condition is one job you can safely take responsibility for.

Although it sounds pretty ominous, bleeding radiators refers to a simple process. It’s about purging, or ‘bleeding,’ air out of the radiators in order to improve the flow of hot water.

Before we get into how to bleed a radiator, we’ll explain when you should bleed a radiator.

DIY: Why Would You Bleed a Radiator?

Bleeding radiators is about ensuring your heating system is working effectively and therefore heating your home efficiently. If your radiators aren’t working as they should, it will take longer for your home to heat up and may end up costing you more money as you need to keep your heating on for longer.

As mentioned above, a radiator should be bled when there’s air trapped inside of it. The air trapped in the system disrupts the flow of warm water around the radiator, preventing it from heating up fully.

Aside from not heating up fully, the main giveaway that a radiator needs bleeding is when the upper half of the radiator is colder than the lower half. Another sign of air being trapped in the radiator is when a knocking, clanking or hammering-type sound is coming from radiators, especially when the heating comes on.

Bleeding a Radiator in 5 Steps

If you’ve identified a radiator that needs bleeding, you’ll need two pieces of equipment - a radiator key and a cloth.

A radiator key is needed to open up the radiator valve. Don’t worry if you don’t have your radiator key as they can be purchased from most hardware shops. Before going and buying any old radiator key, make sure you check the radiator valve (towards the top, on the side of the radiator). Checking the valve shows you what shape of radiator key you need and if you even need one in the first place, as some radiator valves can be operated using a screwdriver.

A cloth is needed to capture any water that comes out of the radiator valve (more on this below).

Step 1: The first step is ensuring that your heating is turned off. It’s not just the thermostat on the radiator your bleeding, the central heating system in your home needs to be turned off. This is a safety precaution - you don’t want hot water spraying out of your radiator when you’re bleeding it.

Step 2: Using your radiator key slowly, open up the radiator valve until you hear a hissing sound. This is the trapped air escaping the radiator. Keeping the radiator key in place on the valve, loosely hold your cloth under or around the valve.

Step 3: When the hissing stops and water starts spitting out of the radiator, quickly re-tighten the radiator valve. Your cloth will stop any water from the radiator hitting you or the floor.

Step 4: Once you’ve bled all radiators that need bleeding, turn the heating back on. Keep an eye on the pressure gauge located on your boiler as bleeding the radiators can affect the pressure of the system.

Step 5: After five minutes of the heating being on, check your radiators to see if they are suitably heating up. Properly functioning radiators should heat up evenly and there shouldn’t be any strange noises coming from them.

If the problem persists, there might be an issue with your central heating system or boiler - it’s best to be safe and get it checked out. Our qualified heating, boiler and gas experts are ready to get your system back to tip-top shape.

You can request a quote using the HandyExperts quick quote system or, if you have any questions, you can call us on 0330 912 2323.

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