How to bleed a radiator without a key

17 January 2023
How to bleed a radiator without a key

How to bleed a radiator without a key

Bleeding a radiator with a flat head screwdriverBleeding a radiator with a flat head screwdriver

Bleeding a radiator is one of the easiest DIY tasks you can carry out when it comes to your central heating. If your heating system is switched on but one of your radiators feel cold at the top or even won't heat up at all, it's likely that air is trapped in the top of the radiator and bleeding out the air could solve your problem.

But what if you've lost your radiator key and are worried that you don't have the right tool to bleed your rad? While radiator keys are readily available at all DIY stores, and most are the same size, that doesn't help if you need to resolve the issue with your heating right now! Fortunately there is another method you can use that will work on many radiators in need of bleeding.

Alternative radiator bleeding methods

If you don't have a radiator key to hand then all is not lost as you might have something else in your toolbox that can help with bleeding your rad. This is important to know as being able to bleed your radiators can help to instantly solve the problems of a cold radiator.

The most popular alternative to a radiator key is by using a flat head screwdriver. Most modern radiators manufactured over the last 5 - 10 years will have a small indent allowing for a flat head screwdriver to be inserted into the bleed plug. Grabbing a receptacle or a cloth to catch any drips, slot in the end of the screwdriver gently turn anti-clockwise. If you have air trapped in your radiators, you'll hear the hiss of the air escaping. Once the hissing stops and water starts coming out, you can quickly tighten up the bleed plug by turning your screwdriver clockwise.

Not all radiators will have the option for using a flathead screwdriver, particularly convector radiators that are quite old. In this situation, it is more difficult to bleed the radiator but not impossible - you can try some other tools such as an allen key, a small spanner or a pair of pliers. However, do be very careful before using any of these implements as you may cause irreversible damage to the bleed plug. Even if you manage to open the bleed valve and allow the air to escape, you may struggle to close it again.

If you don't have a radiator bleed key and your radiator doesn't give you the option of using a flathead screwdriver, consider whether this issue can wait until your can get hold of a bleed key. While frustrating not to be able to solve the issue immediately, a bleed key is designed specifically for this job and will help you clear the issue without causing damage to your radiator. It could really be worth the slightly longer wait rather than opting for a short-term, heavy handed solution.

Are all radiator bleed keys the same?

Radiators installed over the last 30 - 35 years will generally be of a standardised, metric size and you can buy a radiator key that will fit all radiators in your home. They usually have one end that is flat for you to hold between your thumb and forefinger and the other end will be square for you to slot over the bleed valve.

On rare occasions, some houses with very old central heating systems will have radiators that have imperial radiator bleed plugs that modern radiator keys won't fit. These older radiators can still be bled by using imperial clock keys (keys traditionally associated with winding up clocks). A clock key size 12 (4.8mm) will likely be the right size for a very old radiator, though it's worth getting keys in sizes 8 - 12 just to make sure you've got yourself covered.

Whichever type of radiator you've got, it is worth investing in one or two radiator bleed keys. They're not expensive but can be an absolutely vital tool in getting your radiators working properly and heating up your room satisfactorily again.


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