Magnetic filters essential addition to  central heating systems

Fitting a magnetic filter to your boiler can reduce breakdowns whilst increasing efficiency and the life of the boiler. Here is how they do that.


Reduce the risk of boiler breakdowns in winter months for under £200. whilst increasing efficiency and saving money on energy bills 

Heating systems can become clogged and restricted over time with sludge and debris, reducing their efficiency and increasing energy usage. There is a quick and easy way to safeguard and maintain your heating system so that your boiler, pipes, and radiators last much longer and your central heating system continues to heat your home as intended and efficiently. Magnetic filters can help remove this build-up and extend the lifespan of the heating system. Whilst removing debris the magnetic filter can also protect the boiler and heating components from damage and Wear.  If allowed to circulate the debris and sludge within a heating system can lodge within boiler components and create breakdown or leaks. It is however  important to remember that once fitted the filters need to be regularly maintained and cleaned to minimise pass-through of any unwanted materials. If not serviced magnetic filters themselves can suffer from wear and leaks.  

What is a magnetic filter? 

A magnetic filter is a device that collects sludge and debris built up over time in a heating system., Rust and corrosion can develop in pipes over time, and as a result, debris can peel off and join with other debris to form a sludge-like substance. The debris will peel off as the pipes age. This sludge has the potential to generate blockages as well as other problems on the system such as leaks, which will result in the system functioning less effectively and may even lead it to break down. 

The magnetic filter will attract corroded metals, which will prevent a build-up . Because of the filter, water can continue to go through the system as it normally would, and the system can maintain its efficiency for an extended period of time. This device is  fitted to your central heating system and operates with the flow of the water within the system. Magnetic filters for central heating systems attract metallic particles and store them away from your system.  

How do I know if I need a magnetic filter? 

Firstly a magnetic filter is a perfect companion for cleaning wet central heating system, so if you do not have one already fitted it is highly advisable to get the magnetic filter installed as this can only be beneficial for the heating system by keeping it clean and helping it to run efficiently. There are some simple signs to look out for that may suggest that you may benefit from having a magnetic filter installed. Such as: 

  • Noisy boilers or radiators, these can be affected by sludge build up 
  • continuously on the boiler or other parts of the central heating system 
  • Fluctuations in the heating or hot water temperature may suggest blockages in the heat exchangers 
  • partially cold radiators with cold spots could be a signal of sludge and blockages within the system 
  • Frequent breakdown of boiler and components within the boiler  would suggest a dirty or unhealthy system  

Many of these issues left unattended can lead to Bigger problems such as the eventual need to replace the boiler or leaking radiators and pipes.  Whilst  a magnetic filter cannot resolve all the issues  listed above it  can help minimise and reduce the risk of  breakdown and leaks in the future. Severely clogged and dirty systems magnetic filter alarm should not be used as the solution and a much deeper cleanse of the system may be required by means of a power flush 

How do I clean a magnetic filter? 

Regular servicing and cleaning of the magnetic filter is necessary ensure that the magnetic filter is working efficiently. The recommended servicing interval for a magnetic filter is once a year year to remove the debris and rust particles caught up in the filter, however for badly affecxted heating systems a more frequent servicing interval (eg every 6 months) may be more beenficial. This service is usually carried out by a heating engineer during the annual boiler service, but if you competent with polumbing and wish to give it a try have a read through our magnetic filter cleaning guide. 

When should a magnetic filter be fitted? 

Magnetic filters can be fitted at any time in the lifespan of a central heating system. It is best practise to usually fit these during the first initial boiler installation. This helps provide  the best protection for the boiler  in preventing unwanted particles entering the new appliance. A full power flush is recommended during any boiler installation but it’s not usually a requirement by the manufacturer and instead only a cold flush is stipulated. In the majority of boiler installations it’s only the boiler that’s being changed and usually you’re not getting a brand new radiator and pipework system fitted at the same time. This means rust particles, sludge and debris that might be attached to the bottom of the radiators or the pipework can eventually dislodge and travel back to the boiler during use.  A correctly fitted magnetic filter on the return side of the pipework will in most cases grab any of these particles before they enter the boiler and start damaging the components.  Although fitting a magnetic filter at the beginning of installation is good practice it can actually be fitted at any point but it would be good practise to check the quality of the water system to ensure that it is not heavily clogged with sludge. Heating systems badly clogged up mean the filter will fill up very quickly and will stop being effective unless it’s regularly checked and cleaned. However fitting a magnetic filter to an existing system is a good way of minimising further damage to a boiler.  

To what systems can a magnetic filter be fitted? 

Magnetic filters can be fitted to any wet central heating system. Morden 10 years of installing these filters them in combi boilers heat only boilers system boilers heat interface units and electric boilers. Any wet central heating system that utilises metal pipework and metal radiators is prone to Rust and corrosion is rust and corrosion sitting in a stagnated water within the system is likely to create sludge and having a high number of metal particles which can enter the components of the boiler and create lease or other damage. All central heating systems mentioned above work on a flow and return principle where the source heats up the water it flows through pipework and radiators usually with the aid of a pump and at some point the colder water returns into the heating source, This is why a magnetic filter will in principle be suitable for any of these systems. 

Can magnetic filters be fitted to underfloor heating systems? 

Whilst magnetic filters are mostly fitted to central heating systems that utilise radiators they can be fitted to underfloor heating manifold systems. Although it is not very common practise to do so as underfloor heating systems are generally run in plastic tend to be more problematic with build up debris and sludge or rust  products such as the Bastion can be incorporated into underfloor heating systems. Other products such as the Adey Twintech have been developed specifically for underfloor heating systems. These systems often have problems with bacterial contamination due to be made up of plastic components and run at low temperatures. In addition to having  a strong magnetic core it incorporates a stainless steel mesh. This mesh is scientifically designed to remove bacterial contamination from the heating system. A perfect addition to the Adey Twintech is the Adey MC10+ Rapide Biocide which also helps prevent bacterial contamination and algae build up.  

What are the benefits of installing magnetic filters? 

A new central heating system typically includes a new boiler, radiators, pipework, and an accessible thermostat when it is originally installed. Particularly in hard water areas, after a few years issues tend to appear, and these tend to be at the most inconvenient times such as arrival of winter and turning the heating on for the first time. Majority of these issues and breakdowns are a direct result of having sludge within the system. Iron oxide, also known as rust, is the term used to describe the black sludge, which is primarily rust that has broken or fallen away from the interior of your radiators or other central heating system components. Central heating systems incorporating metal pipe works and metal radiators will inevitably create rust particles and sludge within the system. A magnetic filter will help tackle the continuous build up of this sludge and be an effective tool in increasing efficiency and reducing energy costs. Some manufacturers such as Vaillant offer additional warranties on their products if fitted with an approved magnetic filter. Below are some of the main benefits of having these installed.  

  • Will reduce partially heated radiators due to sludge build-up 
  • Will help eradicated reduce noisy heating systems and boilers 
  • Will help reduce leaks in the boiler all the central heating system caused by sludge build up 
  • Versatile and independent device that can be fitted at any stage to a heating system 
  • Can help protect the boiler and reduce costly future repairs 
  • Can reduce energy costs by 6%  
  • No ongoing costs other than the need to service and clean 
  • Convenient access point for addition of chemicals 

Where should magnetic filters be fitted? 

A magnetic filter can be fitted anywhere on the heating system and will be beneficial in providing protection but best practise would be to have it fitted on the return pipe and usually just before the boiler. It is at this point that  can be most beneficial to the heating source i.e. the boiler which will have the most sensitive components in a heating system and is more susceptible to damage and breakdown from sludge within the system. At this point the magnetic filter I can collect all the rust debris and sludge to has been picked up from the radiators and pipework in circulation and can catch these before they enter the boiler.  

How are magnetic filters installed? 

Whilst magnetic filters are a relatively simple device to install, they should only be fitted by experienced and qualified heating engineers. Firstly the correct steps should be taken to install the magnetic filter but more importantly the heating system and the boiler will need initiating correctly and this should be undertaken by a professional. The following are the steps taken during the installation process 

  • Isolate and  drain the water from the central heating system, partially or fully depending on set up 
  • Identify the location for the magnetic filter installation  
  • Mark and remove the section of pipework to accommodate the filter (pipe adjustment maybe required in tight spaces) 
  • Install the magnetic filter isolation valves to the pipework  
  • Securely connect the filter itself to the isolation valves 
  • Check all connections are tight before refilling the system 
  • Check for leaks and remove air from the system 
  • Ensure all the valves are open and test the heating system 

On completion of the installation a chemical inhibitor should be added to the system. As the name suggests this inhibits limescale from forming inside the heating system and the build up of sludge.  

What Are Limescale Inhibitors? 

These are chemicals that stop lime from depositing when water is heated. Limescale inhibitors reduce deterioration of appliances and components such as your water pipe, kettle, boilers, shower, tanks, water heaters, dishwashers and washing machines. . A limescale inhibitor does not, however, physically remove calcium from hard water. A chemical liquid known as a limescale inhibitor works to stop limescale from building up inside the pipes and central heating system of your home. Without a limescale inhibitor for central heating, the heat exchangers is likely to get blocked up and not operate properly. The inhibitor is required  stop sludge build-up before the process can  start.  

Your entire heating system will benefit greatly from using inhibitor in a variety of ways, some of which we’ve already discussed above. In addition to adding inhibitor to brand new installations of a  heating systems, it’s a good idea to also add it to existing system. Although it may not breakdown existing limescale it will prevent future build up. Overtime inhibitors will help in avoiding potentially costly repairs and even an eventual replacement of the boiler. This will also ensure that due to blockages not existing within the system that it heats up quicker and functions more effectively. For existing systems an effective method would be to combine using a system cleaner in order to remove pre-existing limescale build up and then adding an inhibitor in a cleaner system. These can be purchased as a cleaning and inhibitor pack or as complete package  which also includes the magnetic filter.  

How to add limescale inhibitor and cleaner to the heating system? 

These can be added to your system in a number of ways depending on the type of heating system and the set up. Prior to deciding on the correct treatment it may be advisable to use a testing kit in order to get an idea of the water quality within the heating system. 

For combi boilers and sealed systems such as system boilers with unvented cylinders or HIU systems that do not have a magnetic filter installed, directly adding to the radiator is easiest option. Where as in the past these chemical were only available as liquid which would not always been the easiest way to add to a small opening in a radiator, various kits such as Adey MC1 Rapide, the Sentinel X 100 Rapid Dose and the Flomasta Filling Kit use clever attachments to make this job easier and prevent spillage. Other alternatives are using a dosing vessel or products in a tube 

For conventional boiler heating systems that have an F&E tank (usually in the loft) the simplest option is to add the cleaning or inhibitor liquid into this tank.  

For Systems that already have a magnetic filter installed or if one is being added, then the quickest option is to add the chemicals directly to the magnetic filter.  

What happens if an inhibitor isn’t used in a heating system? 

Without adequate inhibitor in a heating system that has metal components such as radiators and pipework, rust particles will build up within the system. Over time this gradual production of rust particles will build up to black sludge causing a number of issues within the system. 

How often should central heating inhibitor be changed? 

The central heating inhibitor should be replaced once a year. Its ability to prevent internal rust build-up and corrosion diminishes over time, therefore new inhibitor should be added once a year. It is recommended that every 12 months, a professional Gas Safe Registered heating engineer should inspect and service your boiler and heating system . Adding a chemical inhibitor to your heating system is typically one of the maintenance procedures performed by a heating engineer as well as cleaning the magnetic filter if you have one installed. 

If the property has been recently purchased or you are unsure when inhibitor was last added to the system, either water tests can be done to check the levels or alternatively you can add more, as adding more than the required amount will not harm the system. Similarly if the system has been drained for any reason the inhibitor should be re-added. If your heating system is drained for any reason in between maintenance checks, inhibitor should be added again. Unless your system has been completely drained down and you are refilling, its advisable to always use the same brand of inhibitor. Mixing different brands may needlessly be mixing chemicals that might create an unwanted reaction within the system 

How much central heating inhibitor should I use? 

You should add a 1 litre bottle of inhibitor for a heating system with up to 10 radiators. The formula should roughly be applied to additional radiators and if unsure slightly more should be added rather than less. It is advisable the system is first fully drained prior to adding as to not mix different types of inhibitors.  

Is it compulsory to have a Magnetic Filter installed  

Fitting an in line filter was according to  BS7593:2019 – Code of practise for the preparation, commissioning, and maintenance of domestic central heating and cooling water systems, was considered Best Practice when installing a new boiler.  

Part L of the Building Regulations has now however changed on June 15, 2022. The portion of Part L that addresses heating in the home is Part L. Building regulations are increasingly requiring the Best Practice document, and when a new boiler is installed, the installer must complete the following tasks:  

  • Perform a system flush and clean.  
  • Fit an in-line filter to the system  
  • Add a corrosion- and scale-preventative inhibitor to the heating system.  
  • In low temperature systems (such as underfloor heating) add a biocide. 
  • During the annual boiler service, the filter must be cleaned, serviced, and the amount of an inhibitor measured in the system water. 


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