As the nights get darker and the weather gets colder, there is one thing we all rely on; our central heating! If you turn on your radiator only to find that it is stone cold, even after 20 minutes or so, it can be incredibly frustrating and worrying, especially as the thought of an expensive repair bill enters your mind.


There are many different reasons why your radiator may have stopped working. We’re going to talk you through them to help you get to the bottom of the problem.

We’ll separate them into two sections to help you diagnose which issues may apply to you:

  • One radiator not working
  • Multiple radiators not working

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One radiator not working

The first thing you need to do is determine whether the issue is with one radiator or several. This will help you get to the bottom of the problem.

Establishing that you have one radiator not working with cold pipes can lead you to do several quick checks. Some of the issues may require professional assistance, yet it could be that the issue is straightforward, meaning you can easily fix it yourself. 

So, let’s take a look at some of the potential issues:

1. Air pockets in the radiator

Have you noticed that the radiator is cold at the top, yet there is some heat at the bottom? If so, this is a big indicator that the issue is simply air in the system.

When this happens, the air takes the space designed for the hot water, preventing correct circulation in the radiator.

You will need to bleed the radiator to fix this. Unscrew the bleed screw using a radiator key until you can hear the air hissing out. Keep going until water appears. When you notice water, tighten the bleed screw.

After the air has been removed, look at the pressure in the boiler system to ensure it is still within the limits. 

2. Radiator thermostat not working properly 

The issue could simply be that the valve for thermostatic radiator control has switched from being set on a temperature to being turned off. 

radiator trv

If a higher temperature has been selected, it would not be unusual for the valves to have seized in a closed state.

This is something you can quickly check by taking off the top cover from the valve. A knurled nut is usually used to secure the valve, and you can undo this with your hand.

Make sure you don’t undo any of the other nuts on the valve, though, or you could find yourself with water pouring out everywhere!

After you have removed the cover from the valve, check that the centre pine can be freely moved up and down by a few millimetres.

If you can’t move it, this means that the pin has seized. Try tapping it gently to free it. If you are unable to do this, you could need to substitute the valve in its entirety. We always recommend getting a professional to do this.

3. Sludge, debris, or blockages

On a rare occasion, you may notice that the radiator is cold at the bottom yet hot on the top. This is an indication that you have debris, a blockage, or most likely, sludge, which has accumulated in the radiator.

Hot water is not able to circulate because of the build-up at the bottom of the radiator.

The most efficient and safest way to deal with this problem is to seek professional help. When you do this, they will provide what is known as a power flushing service.

Power flushing is the process of removing debris and sludge that has become stuck in your central heating system over time and is preventing it from functioning correctly.

Other signs that you may need a power flushing service is if some rooms are colder than others, your central heating takes quite some time to warm up, and you have to bleed your radiators frequently. If you have no or limited hot water, this could also be a sign of sludge build-up, although there are other potential reasons for this problem.

4. A radiator leak

This can be frustrating, as it could mean that you’re going to have to replace your radiator. However, external sealers and leak sealers could assist, depending on the extent of the problem.

Unfortunately, leaks tend to be caused by corrosion, which may mean your system is poorly maintained and needs to be cleaned out and protected. This is the worst-case scenario, though.

A radiator leak from the location where a thermostatic radiator valve connects to a pipe or radiator, or a leak from the pipe joint, may just mean that the nut has gotten loose. Therefore, merely turning it with a monkey wrench could be sufficient to rectify the problem.

Nevertheless, if you have noticed that there is quite a lot of water coming from the pipework, it is evident that a leak is the problem and you are advised to call a professional.

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Multiple radiators not working

If all or several radiators aren’t working, firstly, check your heating is switched on! Yes, we know it sounds obvious, but you would be surprised by how many people panic, assuming their radiators are broken when all they needed to do was flick a switch.

5. Diverter valve fault

If the controls are not working correctly and the pressure is correct, yet there is still not any flow, it could indicate that there is an issue with a diverter valve.

The diverter valve fault is a motorised valve in the bailer that controls the flow of warm water to either your heating or taps. It will prioritise heated water to run to your taps, meaning if you switching your heating on and require warm water from your tap, the valve is going to move the feed to the tap first. 

If you are getting hot water to your taps but not to your radiators, this could be an indication that the diverter valve fault is stuck. This is not something that you should try to fix yourself. You need to get in touch with an experienced engineer who is Gas Safe registered.

radiators control

6. An issue with the central heating controls

Although this problem is rare, it can happen. Issues with the controls mean that your boiler may be working as it should be, and the pressure is within the limits, yet the radiators are not turning on. This could be a problem with the electronic control panel that operates the timing of your central heating and signals to your boiler. 

To see whether this is the problem, check that the timing control is set correctly. Choose the ‘on’ demand to make sure that it heats your radiators.

Beyond this, you are not recommended to change the control panel settings or try to discover the faults. You could end up making the problem much worse and more expensive by doing this. Instead, simply contact a professional who has the experience to get to the bottom of the issue.

7. Boiler pressure is too low

Combi boilers work on a closed-loop system, and they are pressurised to between one and two bar. If your boiler is not properly pressurised, the boiler will not provide the needed hot water to warm your house.

You can find out what the pressure is visually, either via the head of the cylinder, which tends to be located in the airing cupboard or by looking at the front of the boiler.

Should you discover that the pressure is too low, you can turn the top-up valve to increase the water pressure, as this will enable the required amount of water to get in. You do need to be careful, though, as you don’t want too much water to get into the system!

8. A bigger problem with your central heating

Finally, the issue could be a more serious problem with your central heating system, rather than being a problem directly related to your radiators.

You should check to make sure that your central heating is actually working. If all of your radiators won’t heat up, as opposed to just one or a few, this could be an indication that there is a bigger issue.

Check to see if there is anything that seems a bit odd about your central heating system. Do you have hot water or not? Is your boiler making a funny noise? If you have noticed any signs like this, it is essential to get in touch with a professional heating engineer as soon as possible.

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Final words

So there you have it: some of the common reasons for radiator failure. Hopefully, you have gotten to the bottom of the issue with your radiators.

If you are unsure of the problem or don’t feel comfortable rectifying it yourself, you should always call a professional for assistance. A Gas Safe registered engineer will be able to fix the issue safely and efficiently, giving you complete peace of mind.


Skills Training Group are an accredited provider of gas engineer courses and plumbing courses. If you would like any further information, please contact us on 0808 164 2780.

Download your free information pack

Find out how you could train as a domestic gas engineer by downloading a free copy of our information pack.

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