How to manage hot and cold spots in your radiators, central heating problems

How to fix cold patches on radiators at the top, middle or bottom

Cold patches appear on radiators when your water supply is unable to properly flow through your central heating system due to air or substances such as dirt or sludge being present. This means that certain areas of the radiators simply aren’t receiving the supply they need to heat up.


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If the issue is left unaddressed or unnoticed (it is always a good idea to regularly check that your radiators are working properly), it could lead to increases in your heating bills because of the reduced efficiency, which would be wasted money if you aren’t reaping the benefits of the heating itself.


There are a few factors that can cause the radiators in your home to develop cold patches, here are what we believe to be some of the most common causes and their potential fixes:


The top of the radiator is cold

If the top of your radiator is cold, it's possible that there is air trapped within the system. An effective way to release it is by bleeding the radiator, which is a simple fix that can be done in minutes. However, we recommend contacting a qualified engineer if you feel unsure about conducting the job yourself.


All you need is a radiator key, which could be available to buy at a DIY store, and a dry cloth. Be sure to turn your central heating off and wait for it to cool before you proceed to avoid placing yourself at risk.

There will be a valve at the top or on the side of your radiator that should be the same shape as the key. Simply put your dry cloth in place beneath it to catch any water that may escape and insert the key, turning anti-clockwise to loosen the valve.

A hissing noise will start as the trapped air is released and is usually followed by a little water as the radiator returns to normal. Once the air has been released, tighten the valve up again and turn your heating back on at the boiler.

After a few minutes, check that your radiator is heating correctly, and the cold patch has gone. You can read our article on bleeding a radiator to find out more.


The bottom of the radiator is cold 

Radiators that are cold at the bottom could be caused by a build-up of scale, rust or sludge, which obstructs the flow of water. To fix this issue, we recommend you get a qualified engineer to visit your home and conduct a Powerflush.

When the engineer visits your home, they will aim to clear your system of any substances that may be obstructing the flow of water by sending a chemically-infused liquid through your boiler, pipes and radiators at a high velocity.

This process could restore the efficiency of your central heating system and solve your cold patches problem. If you think your system could benefit from a system Powerflush, contact us today and we’ll aim to book you an appointment with one of our friendly, Gas Safe registered engineers at a time that suits you.


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The above information has been provided by HomeServe and is for information only. It is not a substitute for a qualified engineer’s assessment, survey or advice. Undertaking DIY home repairs may pose a significant risk to health and safety where a person is not suitably qualified to undertake such a repair. Boiler repairs should by law always be carried out by a qualified and Gas Safe engineer, so you should never attempt to carry out any repair work on your boiler yourself. Information and other materials on this website are not intended to constitute professional advice and should not be relied upon. Please see our Terms of Use for further details.

Information and other materials on this website are not intended to constitute professional advice and should not be relied upon. Please see our Terms of Use for further details.

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