How To Remove Radiator Sludge

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Our Free Guide On How To Remove Sludge In Your Radiators

Ever wondered why your radiators no longer heat up like they used to? You are not alone. Approximately 20% of Uk homes suffer from dirty heating systems which eventually leads to a build up of radiator sludge and will ultimately lead to your boiler breaking down and costing you money on expensive repairs. We are here to help you prevent this from happening by giving you some advise on what to look out for. If you need to find a heating engineer to help you, click here.

In this blog you will learn: What is radiator sludge and what causes it to build up in the radiators. What are the symptoms of sludge and how we remove it. How to flush your heating system and how to prevent it happening again. Let’s dive in!

What is Radiator Sludge?

The real name for radiator sludge is actually Magnatite. It is a black substance comprised of dissolved and rusted metal from the pipework of your central heating system.

It forms when air and water react with ferrous components , for example if you need to bleed your radiators regularly, you are adding fresh water and mixing it with air within the system which reacts with the steel inside your radiators.

Magnetite is heavier than water and will settle at the bottom of the radiators and in lower levels of pipework such as ground floors and beneath. If the radiator sludge is left to build up it can have a devastating effect to the boiler and the whole heating system. If you would like to read more about Magnatite, click here.


Radiator Sludge

What Are The Symptoms Of Radiator Sludge?

There are a few signs that will tell if you have radiator sludge and you do not need to pay for a plumber to confirm this.. First turn on your heating and leave in for 10 to 20 minutes depending on how many radiators you have. The water needs to find it’s way around the system before all the radiators get hot. By placing your hand at the bottom of each radiator you will feel if you have cold spots. If there are cold spots, there is a high probability that you have sludge in your radiator.

If the bottom of the radiators get warm but the top is cold, you have air trapped and just need to bleed the radiator.  You just need to use a bleed key to release the air from the system. Don’t forget that you will need to add water to the heating system via the filling loop at the boiler.

If you bleed your radiator and notice that there is brown or black water coming out this is another sign that you might have sludge in your radiators.  In this instance, you would benefit from removing the sludge to prevent future issues. If you do not feel comfortable doing this, contact a heating engineer and they will come out and remove the sludge from your radiators.

Another sign that you have sludge in your radiators/heating system  would include the boiler and the circulating pump making noises or causing the boiler to shut down due to overheating. This is not something that you will be able to replace yourself as you will need a Gas Safe Registered engineer to do this for you.

radiator valves


How To Remove Sludge From A Radiator

It is relatively straightforward to remove sludge from a radiator. However, if you do not feel comfortable with this, please contact your local heating engineer.You will need some old dust sheets, a wrench, a bucket, radiator bleed key, rubber hammer and a hosepipe. To get started you will need to turn off your heating and let it cool down. Have your dust sheets directly underneath the radiator that you are taking off the wall to protect the carpet from getting any sludge on it. Radiator sludge can be messy so please ensure that you do put down enough sheets on the floor before proceeding!

Next, close off both sides of the radiator valves. To do this, you will need to start by turning off the thermostatic radiator valve (TRV), which is done by twisting the head to either the ‘0’ or ‘off’ position.

You will find the lockshield valve on the other side of your radiator. In order to turn this off, you will need to remove the plastic cap and then use a wrench to turn it clockwise all the way. When doing this, a handy tip is to count how many turns it takes you to turn off the valve; note this down, as it will give you an indication of how to re-balance the radiators after flushing.

Next you have to drain a radiator but before doing this, you need to place the bucket underneath the thermostatic radiator valve (TRV).

With a wrench in each hand, use one to grip the valve’s body and the other to loosen the nut between the radiator and the valve.

Next, slowly open the vent plug with the bleed key and you will see water flow out and into your bucket. Next loosen the lockshield and tilt the radiator to allow the remaining water to come out. Once the radiator is emptied, don’t forget to use the key to close the bleed valve.

Now that the water has been emptied, you will need to remove the radiator from the wall and from its brackets. A small tip: Once the radiator is removed, turn it upside down so you won’t drip any sludge on your carpet when you are taking it outside to flush. Do NOT attempt to flush the radiator inside the house!

Once in the garden, attach your hose pipe to the inlet of the radiator valve and switch the water on at full power, thoroughly flushing the inside. The pressure of the water should be enough to push out the sludge.  You can use a rubber hammer to try and dislodge any excess build-up. Try flushing the radiator into a drain if possible as you will not want and sludge to get on your lawn.

Continue to flush out the radiator aludge until the water from the inlet on the other side is completely clean.

Once you have finished flushing the radiator you can reconnect it in reverse order. Ensure to re-tighten the nuts, open both valves and turn the lockshield valve the same number of times you noted down beforehand.

Finally open the bleed valve to allow any air trapped inside to escape. Dont forget to top up your boiler pressure at the filling loop. It should be between 1 and 1.5 bar.

Boiler pressure guage


How To Flush A Heating System

If after flushing your radiator/s using the above method doesn’t work properly and your radiators are still not heating up correctly, it is time to call a professional heating engineer to come and flush your system to remove the radiator sludge. Sometimes there is just too much build up of Magnatite stuck at the bottom of the radiatiors that wont release by just flushing cold water through it.

If you need more information on how a heating system is flushed, please click here to see one of our recent blogs on this. It is vital that any build up of radiator sludge is identified early to prevent any permanent damage to boiler components or likewise any radiators.


How To Prevent Radiator Sludge

Although it can sometimes be difficult to identify radiator sludge, you can take some preventative measures to help reduce any build up of sludge in your system. The easiest way to check is if you notice your radiators are not heating up correctly, check for radiator sludge straight away (by using the above methods) before it has the chance to accumulate. Another good preventative measure is to have your system flushed every 5 years or so as this is the average lifespan of central heating inhibitor which is added to the system to prevent radiator sludge from building up.

Another helpful tip is to ensure that your annual boiler service is carried out by a competent gas engineer that should also check the water quality in your heating system as part of the service.



We hope that you got some good value from this blog and now have some knowledge of what you should be looking out for on how to identify a build up of radiator sludge. It is extremely important to catch a build up of radiator sludge at the early stages before it gets out of hand. If left unnoticed or unattended, radiator sludge has the potential to ruin the complete heating system which could potentially cost thousands to replace. If you are looking to replace your boiler, click here for a quote.






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