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Witten by Bernard Morgan (Engineer) & Adam Apperley (Marketing). Published: August 2, 2019. Updated: January 23, 2024

Why is my radiator not working? | Central Heating Solutions

Any kind of issues with your current central heating system can be frustrating. Many people may think of the boiler itself as the primary source of heat, but even if you have just one radiator not working, your whole heating system is affected and must be addressed.

For this article, we’ll be tackling some of the ways your radiator could be affected by an issue, including:

  • The top of the radiator is cold
  • The bottom of the radiator is cold
  • One radiator not working

An unchecked problem like a radiator not working can affect your pipework, other central heating radiators and of course, your boiler. For instance, a build up of magnetic sludge, can dry up inside your system, often meaning you’ll have to invest in completely new pipes. You could also damage your boiler’s heat exchanger, your energy bills can rise and your home won’t be comfortably heated.

If you’re looking for a new boiler replacement, find out which boiler is best for you and your property by going through some of our previous articles:

If you find yourself dealing with a radiator not working often, you may need to look into replacing your boiler. To find out how this can be done, scroll down to the bottom of the page!

If you’re looking to replace your radiators or central heating system, speaking to one of our in-house experts can help you understand your options and how to move forward on a new boiler quote. Just call us up on 029 2009 9898 or get a free, no-obligation quote by entering your postcode in the box below, then click the green button.

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Why is my radiator cold at the top?

Do you find different parts of the radiator more heated than others? Does the bottom feel well-heated but the top is ice cold? It’s likely because it has trapped air inside, taking up space that would otherwise be used by water to warm the radiator up.

Your radiators work alongside your boiler to ensure your home is comfortable heated. If your radiators aren’t working properly however, you’ll just be throwing money away, and who wants that?The good news is that you can perform a radiator bleed as a quick and easy-to-perform solution. Doing this small task can help your central heating radiators perform as efficiently as possible, saving you money on your energy bills.

Why is there air in my radiator?

A likely reason for this is that you have a small leak somewhere on your radiator. This can build up over time before any evidence is even noticed, which itself is often the cause for a radiator not working. This is also something you may notice if you often have to repressurise your boiler.

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How to Bleed a Radiator

For a quick breakdown on how you can bleed your radiators, take a look at our short video:

What you need

To perform a radiator bleed successfully and safely, you’ll need the following:

A radiator key – Pretty important for the whole process. You could try it with pliers but you may risk damaging the central heating radiator, which you don’t want to do. They’re issued with each radiator, but any regular DIY shop will keep them in stock as well.

A cloth or towel – Have this around your hands when you turn the key to bleed the radiator. For a radiator not working, this will keep your skin safe from any nasty chemicals, and make sure everything is kept dry for the whole process. As well as this, keep a towel ready by the end of the radiator, it’ll prevent any spillages landing below while you’re bleeding your radiator.

Steps for how to bleed a radiator

1. Turn on Central Heating to find out which radiators need bleeding

You might need to bleed more than one radiator, so make sure you’ve gone through all of them to save time later on. If they’re across multiple stories, start with the ground floor radiators, and then work your way up.

Once they’re heated up, locate the cold patches by gently moving your hand over the surface, but make sure you wear gloves for safety. If it’s cold near the top, then this will be the air that you’ll need to bleed out.

2. Turn off Central Heating and wait for it to cool

Now that you know where your cold patches are, you can turn the central heating back off. Don’t forget that your radiators will still be hot so wait as long as needed to until they’re completely cool. If you try it while the central heating is on, air will be sucked back into the system, creating more work. As well as this, hot water may spurt out which can be dangerous if you’re working close to the valve. If you wait for the water inside to settle and cool, the bleed will be much more effective.

3. Find the bleed valve and turn using the radiator key

radiator valve turn on

The bleed valve is a small square inside a round hole, found at the top of your radiator on either end. Using the cloth for extra grip, insert your radiator key over this opening, and turn anti-clockwise. You’ll barely need to turn it 45 degrees for it to do the job. If you keep turning it all the way, the water will reach you faster and it will be much more difficult to stop.

Once you’ve started turning it, you should hear a distinct hissing noise.

4. Wait for the hissing to stop

The length of time depends entirely on how much air is trapped inside the radiator, but it rarely goes beyond a minute. As soon as you hear the hissing start to disappear, be prepared to catch the water that will soon follow. Once all the air has been released, the valve will start to trickle water which can be mopped up by the cloth you’re holding underneath.

If you want to be certain there’s no more trapped air, wait until you get a steady stream of water out the end. Just be prepared with the towel!

5. Re-tighten the valve

radiator valve turn off

When turning the key clockwise, make sure not to over-tighten. The last thing you want is to damage the valve.

Once this is done, use the cloth and simply wipe away any excess water that dripped out during the bleed. Doing this not only tidies it up and prevents any slipping, but it helps to stop any rust grow over time.

6. Turn the heating on again

Now that you’ve gone through all your central heating radiators and bled the air out, as long as the valve has been closed shut, it’s now safe to turn the central heating back on. This will be the best way to check that it’s worked. The radiator panels will feel hot all over with no leaks or drips from the bleed valve.

Gently place your hand over all parts of each radiator, and try to find any remaining cold patches. For the most part it will have done the job straight away, but don’t be afraid to try it more than once.

Final Checks for bleeding a radiator not working

Don’t forget, you’ll also need to check your boiler’s pressure to make sure it’s at a reasonable level. This would typically be around 1.4 bar, but by bleeding air out of the radiators, you’ll have lowered the pressure. If it’s fallen too low, you may struggle to get heat in some of the upper floors.

If this is the case and you’re working with a combi or system boiler, simply top up the pressure by using your boiler’s filling loop. You can learn how this is done but clicking here. However, this is not something that you can perform with an open vent boiler.

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Why is my radiator cold at the bottom?

A radiator that’s cold at the bottom can catch a homeowner off guard if it’s not dealt with straight away, especially during the colder months. The most likely reason for this kind of problem, that you have a build-up of magnetite sludge.

What is magnetite sludge?

The sludge that can build up in your radiators is usually a mix of limescale, magnetite sludge and dirty heating water. If you don’t have any filters installed, this can build up quickly.

Limescale is a hard, white substance that comes from natural minerals in water. It’s mainly made up of calcium carbonate and can be every plumber’s worst nightmare. To establish the level of limescale in your area, ‘water hardness’ labels are assigned to all areas in the UK.

water hardness can help solve your radiator problem

Dirty water in your system occurs as a result of rust breaking away from inside central heating radiators, pipework and towel rails.

When it builds up, the flow of water around the radiator is restricted, making heating difficult and costly. This is similar to how the human body works. If a diet is full of fats and sugars, arteries can get clogged up which restricts flow to the brain and the rest of the body. Once your pipework and radiators are clogged with magnetite sludge, it’ll affect your entire heating system.

As water gets pumped through your system, it passes different metals like brass, copper, and steel. When an electrolysis breakdown occurs, your steel radiators will be attacked first, causing internal corrosion. This is similar to the hull of a boat traveling through the water – while being an incredibly well-designed piece of engineering, components will still need to be protected and preserved.

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How to respond if your radiator is cold at the bottom

1. Find out which radiators have the problem

Magnetite sludge is heavier than water, so the lowest radiator in your property is going to be affected first. To find out if others are affected, you can begin by turning the heating on, then running your hand gently along the radiator’s surface.

Touch your radiator gently to find the cold patches

Moving your hands gently across the radiator surface allows to safely assess where the cold patches are

2. Arrange a flush of your system

Because you now know which radiator contains a sludge build-up, you have other options available for you. You can perform one of several types of flushes:

  • Standard Chemical Flush
  • Power/Advanced Flush
  • Mains Flush

When arranging a flush of your system, you’ll need to consider the age of your property. For instance, a power flush could cause damage if the system is too old, so another option like a chemical flush is often a better choice.

3. Apply a chemical inhibitor to your heating system

Adding a central heating inhibitor is very important because it helps to reduce the chances of an electrolysis breakdown in the system.

a typical chemical inhibitor used when a radiator cold at bottom

This is a typical chemical inhibitor used to clear out your system in a chemical flush

Types of Central Heating Flushes available

What is a chemical flush?

For this type of flush, a professional will send the chemical through your central heating system, breaking down and disperses the sludge that accumulates over time. Once done, you’ll have a final flush before adding chemical inhibitor, giving your system that much-needed clean. The benefit of chemical flushes is that they’re perfect for breaking down the sludge in older properties with weaker systems. The cost is usually lower, and can ultimately save you money in the long run by improving your boiler’s longevity.

We believe a chemical flush is the most cost-effective way to get your system clean.

What is a Power Flush?

To carry out a power flush, a professional will need to visit the property. They’ll begin by attaching a pump to your central heating system. From here, chemicals will be pushed through the radiators, pipework and boiler at high speed. Any deposits from the system are then collected and removed.

What is a Mains Flush?

If you’re unable to pay for a professional power flush, a mains chemical flush may be the best option for sorting out a radiator that is cold at the bottom.

To carry out a mains flush, you need to:

  • Have towels ready – Use these to avoid any splash damage or stains.
  • Turn the radiator valves off – Start by turning the temperature control valve by hand, then use a wrench to turn the lockshield valve (the one on the other side of the radiator). Remember how many times you need to turn them, you’ll be doing the reverse later on.
  • Loosen the nuts connecting the radiator valve
  • Open the bleed valve with a radiator key – Use a bucket or any container to catch everything that comes out of the radiator. Once completed, close the bleed valve back up.
  • Remove the radiator – Once you’ve disconnected it from the wall, take the radiator somewhere safe so you can hose it through (gardens are usually best).
  • Hose through the radiator – With the hose over one end, turn your taps on so that water is flushed through the radiator and coming out the other side.
  • Reconnect it to the system – After you’ve flushed the system with water, you can reattach the radiator using the same number of turns on the valves as before.
  • Check the boiler pressure – If the boiler pressure is too low, you can repressurise if required.

a typical chemical inhibitor used when a radiator cold at bottom

This is a typical chemical inhibitor used to clear out your system in a chemical flush

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How can I stop my radiator from not working?

Thankfully, there are things that you can do to help your central heating system and lower your energy bills:

  1. Have a filter installed – If you’re in the process of arranging the installation of a new boiler, these are a must. Using filters like the Spirotech UE022WJ Magnetic Filter, they’ll work hard to catch any sludge that is deposited into the system.
  2. Use a chemical inhibitor – As mentioned, adding a chemical inhibitor to your system helps prevents corrosion and the buildup of sludge
  3. Use a deaerator – When you’re using your central heating, air gets passed through the system as well as dissolved oxygen. The deaerator removes this by sucking it out. A good example is the Spirovent RV2 22mm Deaerator, which you can see below.
Spirovent RV2 22mm Deaerator

Spirovent RV2 22mm Deaerator

How to get a free online quote

While there are many who simply need to bleed their radiator once to get their heating back, others may have to tend to this problem far more frequently. This can happen if a central heating system is quite old, as it means the pipework and central heating radiators have gone unchecked for a long time, allowing a build of sludge.

If you’re looking into replacing your boiler or central heating system, you can find all the answers and support you need by calling us directly on 029 2009 9898 to speak to one of our in-house heating professionals. On top of this, you can also get a free, no-obligation quote online by entering your postcode below, then hitting the button…easy!

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