Are Magnetic Filters for Central Heating Worth It?

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Last updated: October 31, 2023

You want your boiler and central heating system to run smoothly, but over time, debris, limescale and rust can build up inside the pipes and compromise the system’s efficiency. And if left untreated for too long and your problems can also build up, eventually leading to a potential boiler break down, which is something you want to avoid.

To prevent serious sludge build ups in your central heating, you need to keep it well serviced, cleaned and maintained. And one way to help do this is to install a magnetic filter. But what does a central heating magnetic filter do and is it worth it? We give you the lowdown.

What is a Magnetic Filter?

In any central heating system, debris can build up in the pipes over time for a range of reasons. Particularly if you live in a hard water area, limescale – a hard chalky deposit mainly consisting of calcium carbonate – can build up, especially on your boiler’s heat exchanger, reducing its efficiency and causing potential blockages. Water passing through your metal pipes and radiators can also contribute to the formation of internal rust. Limescale and rust, combined with general dirt and debris can then form into a mud-like substance, commonly known as sludge. As this sludge moves with the water flow through your central heating system it can settle and build up, causing a whole host of potential component problems as well as poorly performing radiators and boiler.

To slow down the formation of this sludge and to minimise any potential damage, you can decide to have a central heating magnetic filter installed. Magnetic filters work by attracting metallic particles, including corroded iron and steel, that are found in sludge and by taking them out of your system, the water can flow freely without obstruction. You can also get magnetic filters with a gravity filter to remove non-ferrous debris.

A small cylindrical unit, a magnetic central heating filter is fitted to the return pipe of your boiler so that unwanted sludge is prevented from entering the central heating system and potentially saving you money on unwanted repair bills, as well as extending your boiler’s lifespan.

Why Do I Need a Magnetic Filter?

Magnetic filters can be an effective way of helping to minimise sludge build up and so keep your boiler and central heating system running smoothly. But they may not always be necessary, for example, if you have had your system recently treated with a corrosion inhibitor. However, if you suspect that sludge, limescale, dirt and debris is starting to clog your heating system, then these magic magnetic filters could be a good option. And adding one to your system after you have had the central heating powerflushed is advisable so you can keep the newly flushed out system working cleanly for longer.

Signs that your central heating system could do with a little magnetic help to tackle the issue of sludge build-up include:

Cold spots on your radiators – if you are finding some or all of your radiators have a tendency to remain cold at the bottom but hot elsewhere, this can indicate a sludge issue as the hot water is being prevented from reaching all of the radiator. Finding you are having to regularly bleed your radiators to release trapped air is also another giveaway.

An overheating boiler – if you are finding your boiler is getting too hot and or the pressure is too high and so shuts itself down, then debris and grime could well be to blame. If your central heating becomes too clogged up, it can create back pressure and compromises the pump seals. This pressure can trigger your boiler’s safety function so that the boiler is locked out or shut down.

Your boiler is making ‘kettling’ noises – if your boiler starts to make a sound that is similar to a boiling kettle – known as ‘kettling’ – then sludge and limescale could well be the culprits. Limescale, especially if it collects on the boiler’s heat exchanger, can cause a blockage that restricts water inside your boiler. This means that the hot water doesn’t flow as it should out of the boiler but is kept inside for longer than it should, heating up all the time. The steam that is then produced creates pressure inside the boiler, making those boiling kettle sounds.

Increased energy bills that don’t quite correspond with usage – if sludge is left untackled and is left to build up in your boiler and central heating, the system will eventually be unable to work as efficiently as it should, increasing your home’s carbon footprint and running the risk of higher energy bills.  Then there is the risk of significant internal damage and expensive repair bills, as well as the lifespan of your boiler being potentially reduced.

However, there are numerous benefits of fitting a magnetic boiler filter to your potentially sludge-clogged central heating system, including:

  • A system that consistently and reliably warms your home
  • A more energy-efficient heating system and so potentially lower energy bills
  • Reducing the likelihood of the need for expensive boiler or central heating system repairs
  • A longer boiler life before you need a new replacement boiler
  • A reduction in your home’s carbon footprint

Can I Add a Magnetic Filter to my Existing Heating System?

A magnetic filter is always fixed to the return pipe, which is the pipe that returns water back to the boiler once it has travelled around your central heating. In most cases, the filter is added to a new boiler during its initial installation and therefore can be replaced.

Adding a magnetic filter to your existing heating system can be done but it does depend on where your boiler is located in your home.  Retrospectively fitting a magnetic filter to an existing boiler can be tricky if there is not sufficient space to install it or the pipework may not be easily accessible.

If you are looking to get a magnetic filter, the best thing to do first is to call out a gas safe central heating engineer. They will be able to assess your boiler and the pipework and tell you if it is possible and beneficial for your particular central heating system. If it is possible, the installation should take no more than a couple of hours and by helping to protect the boiler and central heating, can save you money in the long run.

Do Magnetic Filters Require Cleaning?

As with all the various mechanical parts and components of your central heating system, a magnetic filter will need a level of maintenance to keep it in efficient working order. And this means keeping it clean. Due to the nature of the sludge the filter collects, it is advised that the unit is cleaned once a year so that the collected sludge can be completely removed. A full magnetic filter will have diminished working capacity, and you run the risk of your boiler and heating being overwhelmed by sludge build up despite the filter being in place.

For ease, it is recommended that you incorporate a magnetic filter clean as part of your boiler’s annual service so it can be conducted by a qualified heating engineer. And you may need to initially have the filter cleaned a little more frequently if your system has recently had a full powerflush or you are aware of a significant sludge build up.

Is a Magnetic Boiler Filter Worth it?

Whether you have it installed at the same time as a new boiler or fitted to existing boiler and heating system, there is a cost to adding a magnetic filter to your home. But when you weigh up the benefits of having a filter, then on paper it is certainly worth it. But this does come with a couple of caveats:

The magnetic boiler filter will not completely clean out your heating system, especially if it is suffering from a significant sludge problem.

To get to the root of your boiler build-up issues, the magnetic filter works well in conjunction with other measures, including annual servicing, limescale inhibitors and periodic system flushing.

A magnetic filter can extend the life of your boiler for an extra few years, but there are other signs and symptoms which indicate general wear and tear, and which can also lead to a boiler breakdown if not resolved.

But when you consider the time and money you could save, then if your central heating system can accommodate a magnetic filter, then it does make sense to get one installed.

And if you are getting a new boiler, then always check with your installation engineer that a quality magnetic filter is included, so your central heating has that extra protection from sludge build-up from the get-go.


  1. Are Magnetic Filters Worth It? Boiler Filters and Limescale Inhibitors Explained – BOXT