How to bleed your radiators

As winter starts to set in, the chances are you’ve already fired up the central heating. But if your home isn’t feeling as toasty as it should, it’s probably time to bleed your radiators. Sure, you could turn up the thermostat, yet this wastes fuel and could earn you hefty bills as your boiler will simply have to work harder to achieve the right temperature. While bleeding radiators is admittedly not the most fun household task, it’s easy and quick and having your house warm again will make it well worth the hassle.

Why do you need to bleed radiators?

A natural side effect of the heating and cooling of water is the production of air bubbles. Within your central heating system, there is nowhere for this trapped air to escape. The bubbles rise to form larger pockets of trapped air which displace the water in your radiators. Because air does not conduct heat as well as water, you might notice these air pockets as cold patches on your radiators. At this point, the central heating system will have become inefficient and your home won’t reach the desired temperature without turning the thermostat up. If you don’t bleed your radiators, the problem will worsen. Eventually, your central heating won’t get to the correct temperature, even with it turned right up.

When should you bleed your radiators?

With the production of air being a natural process of the central heating system, bleeding your radiators is one household task you’ll have to do on a regular basis. As a guide, bleeding them twice a year should keep them kicking out plenty of heat. If you’re not sure, feel for cold patches on your radiators, particularly near the tops. If you find any, you need to bleed your radiators. Maintaining your central heating system by bleeding radiators will keep your home snuggly warm and your energy bills as low as possible. You can bleed your radiators at any time of year, but winter is the best time as with the heating on, you’ll be able to identify problem radiators more easily.

Should you bleed radiators if you have a combi boiler?

You can bleed radiators yourself if you have a combi boiler, but be aware that sealed central heating systems like those with a combi boiler need to be re-pressurised after bleeding radiators. This is done with a lever or valve located near the water supply to the boiler. The process will be detailed in the boiler instruction manual. If there are no instructions or you are not familiar with topping up the pressure in your boiler, you should call in a professional to bleed your radiators.

What do you need for bleeding radiators?

A radiator key or flathead screwdriver

Depending on the type of bleed valves on your radiators, you’ll either need a radiator key or a flathead screwdriver. Most radiators are bled using a radiator key but if you’re not sure, find a bleed valve. They are located on the left or right side of the radiator at the top. A bleed valve on an older radiator looks like a hole with a square bit in the middle. On some newer radiators, the bleed valve has a straight groove for a flathead screwdriver.

Old cloths

When you open the bleed valve, the pressure inside the central heating system will force out the trapped air. When all the air has escaped, water will start to come out. You’ll need to press an old cloth against the bleed valve as you open it to minimise mess. It’s also a good idea to place more rags on the floor underneath to catch any stray drips.

How do you bleed radiators?

So you’ve got your radiator key and rags at the ready – what now? Let’s find out how to bleed a radiator:

Step 1: Turn the heating on

Step 1: Turn the heating on - How to bleed a radiator | First Utility

The heating mustn’t be on when you actually bleed radiators but it needs to be on for a while before you start. When it’s been on long enough that the radiators should have warmed up, check each one for cold patches. Make a note of any with cold spots as these are the ones you’ll need to bleed.


Step 2: Switch the heating off

Step 2: Switch the heating off - How to bleed a radiator | First Utility

The system needs to have warm water in it for bleeding radiators, so switch the heating fully off and wait for the radiators to cool a little. About 20 minutes should be perfect – the time it takes to sit down with a cuppa and a biscuit.


Step 3: Prepare the area with old cloths

Step 3: Prepare the area with old cloths - How to bleed a radiator | First Utility

Place some old cloths on the floor underneath the bleed valve to catch any spills.


Step 4: Open the bleed valve

Step 4: Open the bleed valve  - How to bleed a radiator | First Utility

Put the radiator key in the bleed valve and hold a rag around the valve with your other hand. Turn the key anticlockwise about half a turn until air hisses from the valve.


Step 5: Wait for water to come out

Step 5: Wait for water to come out  - How to bleed a radiator | First Utility

When water starts to trickle out of the valve, all the air is out. Turn the radiator key about half a turn clockwise to close the bleed valve. Be careful not to overtighten it as this can damage the valve.


Step 6: Wipe up any drips

Step 6: Wipe up any drips  - How to bleed a radiator | First Utility

If any water remains around the valve area or has dripped down the radiator, wipe it with a dry cloth to prevent rust.

Repeat steps 3 to 6 for all radiators with cold patches.


Rather get someone else to do it? That’s understandable and we know just the people to help. First Utility Home Services, brought to you in partnership with Bizzby, puts you in contact with local, expert tradespeople. They can help you maintain your home's heating, from bleeding radiators to carrying out gas safety checks.


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