The Best Central Heating Filters For Every Boiler System
Magnetic filters that sit on the return pipe and keep sludge out of your boiler.
Our quick verdict
Our pick of the best central heating filter is the Magnaclean Professional 2 Magnetic Filter. Its compact body fits the cramped space under a wall-hung boiler, it comes in 22 or 28 mm, and the Professional on our own pipework has given us no complaints. For awkward 22 mm pipe runs, the Fernox TF1 Central Heating Magnetic Filter fits whichever way the pipes run under the boiler.
DIY Works is reader supported. If you buy through our links we may earn a commission, which never changes what we recommend. How we make money.
Our Picks At A Glance
- Check price of Magnaclean Professional 2 Magnetic Filter
Best Overall
Magnaclean Professional 2 Magnetic FilterMost combi and system boilers where space under the boiler is tight
- Check price of Fernox TF1 Central Heating Magnetic Filter
Best Versatile
Fernox TF1 Central Heating Magnetic FilterAwkward installs on 22 mm pipework running vertically or horizontally
- Check price of Boilermag Domestic Heating System Filter
Best Budget
Boilermag Domestic Heating System FilterBudget installs that still want a long warranty and a full kit
- Check price of Worcester Greenstar Central Heating System Filter
Best Quality
Worcester Greenstar Central Heating System FilterWorcester boiler owners who want a filter built around easy servicing
- Check price of Altecnic Dirtmag IQ Magnetic Sludge Filter
Best All-Rounder
Altecnic Dirtmag IQ Magnetic Sludge Filter22 mm systems that suffer with trapped air as well as sludge
- Check price of Boiler-m8 Defender Magnetic Filter
Best Budget Runner-Up
Boiler-m8 Defender Magnetic FilterThe cheapest way to add a filter to a 22 or 28 mm system
Fit decides more than the magnet does with a central heating filter. Check whether the return pipe under your boiler is 22 or 28 mm, as half the filters here only come in 22 mm, and see how much room the boiler cupboard leaves, since a compact or any-angle body saves rerouting pipes.
Servicing matters next, because a filter only helps while someone cleans it, and each clean drops the pressure a touch, so it pays to know how to repressurise a boiler. Our six run from budget kits to a filter built around Worcester boilers.
How We Judged These Central Heating Filters
Between our homes and the rentals and Airbnbs we manage, we have several boilers to look after, and over the years we've had magnetic filters fitted on new boiler installs and during services. A heating engineer has always done the fitting, but we ask them about the install every time and ask to see what the filter has collected when they clean it at the annual service.
That service check tells you more than any spec sheet. The two photos below come from a recent service at one of our rentals, where a Fernox TF1 Compact had been on the system for a year. The magnet came out caked in black sludge that would otherwise have been going round the boiler.
When a brand brings out an improved filter, we ask for the older one to be swapped at the next service. The next two photos show MagnaClean units from our own systems, a Professional sitting in its box with the valve spanner and a smaller MagnaClean Micro already in place on the pipework.
Alongside what we've seen come out of our own filters, each one in this roundup was judged on these points:
- Capture: how it deals with magnetic sludge and whether it also catches non-magnetic debris
- Installation: the pipe sizes it comes in, the angles it can be fitted at and how much space it takes under the boiler
- Servicing: how easily an engineer can isolate, drain and clean it
- Hardware: which valves, spanners and fittings come in the box
- Backing: the standards it meets and the warranty behind it
- Value: how the price compares with the rest of the list
Our Pick Of The Best Magnetic Central Heating Filters
All six filters below work with standard combi and system boilers. Check your pipe size before ordering, as two of them only come in 22 mm.
Best Overall
Magnaclean Professional 2 Magnetic Filter
Best for: Most combi and system boilers where space under the boiler is tight
Check Price On AmazonThe MagnaClean Professional is the filter we have on our own pipework, pictured at the top of this page, and since it went on we've had no complaints. The Professional 2 listed here is the updated version, and Adey designed it with a compact body so it fits the cramped space under a wall-hung boiler, which is where installers tend to run out of room.
Inside, a twin reverse flow design moves the water past the magnet in a way Adey says improves debris capture. For the installer, Adey says an in-line fit takes 2 minutes and it suits all boiler types, in 22 or 28 mm. The low-profile drain valve keeps the annual clean quick, and the box covers the fitting itself with the isolation valve fitting, lid and valve spanner, along with an installation guide, warranty card and labels.
What we like
- Compact body for tight spaces under the boiler
- Twin reverse flow design for better debris capture
- In-line install in 2 minutes according to Adey
- Suitable for all boiler types
- Made in 22 and 28 mm versions
- Low-profile drain valve for servicing
What to know
- Costs more than the Boilermag and Boiler-m8 filters
Our verdict
For most homes the MagnaClean Professional 2 is the safe choice, with a compact body that suits almost any boiler and both common pipe sizes. Adey's Professional 3 adds WiFi for remote monitoring, which isn't worth the extra for most homes, and the Boilermag Domestic does the job for less money.
Best Versatile
Fernox TF1 Central Heating Magnetic Filter
Best for: Awkward installs on 22 mm pipework running vertically or horizontally
Check Price On AmazonOur service photos show a TF1 Compact, the smaller model in the same Fernox range as the TF1 listed here, after a year in one of our rentals, and the amount of sludge on the magnet is the clearest proof we have of what these filters do. Without it, all of that would have been circulating through the boiler and radiators.
What sets the TF1 apart is how it fits. It goes on vertical or horizontal pipework, so the installer isn't stuck when the pipes under the boiler run the awkward way, and the dosing point is easy to reach for adding inhibitor. Fernox describes it as a hydro-cyclonic and magnetic in-line filter, with the cyclone separating non-magnetic debris while the magnet holds the iron particles, and says it cleans in seconds without coming off the pipe. Valve fittings, rubber washers, instructions and labels come in the box. The limit is pipe size, as it's only made for 22 mm.
What we like
- Separates magnetic and non-magnetic debris
- Fits vertical or horizontal pipework
- Easy-to-reach dosing point for inhibitor
- Cleans in place according to Fernox
- Valve fittings and rubber washers included
What to know
- Only made for 22 mm pipework
Our verdict
Fit the Fernox TF1 when the pipework under the boiler runs in an awkward direction or you want quick cleaning at each service. Our service photos of its smaller sibling, the TF1 Compact, show how much sludge the design catches in a year. It only suits 22 mm pipe, so a 28 mm system needs the MagnaClean Professional 2, the Worcester Greenstar filter or the Boiler-m8 Defender.
Best Budget
Boilermag Domestic Heating System Filter
Best for: Budget installs that still want a long warranty and a full kit
Check Price On AmazonBoilermag's Domestic filter costs less than the big names but still extracts both magnetic and non-magnetic debris. Like the TF1, it can go on pipework at any angle, which makes life easier for whoever is fitting it.
The three-year warranty is the standout at this price, beating the two years on the Dirtmag and Boiler-m8 and the 12 months on the much dearer Worcester filter. The box is well stocked too, with the filter, brass isolation valves, valve seats, a bowl spanner, a pipe cut template, a magnetic core remover, security seals and labels.
Where it falls behind is build quality, which isn't up to the MagnaClean or Worcester units. For a rental or a tight boiler budget, that's a fair trade for the price and the warranty.
What we like
- Three-year warranty
- Fits pipework at any angle
- Extracts magnetic and non-magnetic debris
- Brass isolation valves and bowl spanner included
- Pipe cut template and magnetic core remover in the box
What to know
- Build quality isn't up to the MagnaClean or Worcester filters
Our verdict
A full kit in the box and a three-year warranty at a budget price is a strong combination, and it makes the Boilermag Domestic a sensible choice for a rental or a budget boiler swap. Build quality is where the savings show. If you can spend more, the MagnaClean Professional 2 is the better-made filter.
Best Quality
Worcester Greenstar Central Heating System Filter
Best for: Worcester boiler owners who want a filter built around easy servicing
Check Price On AmazonWorcester is one of the biggest boiler makers in the UK, and its Greenstar filter carries the same premium pricing as its boilers. It's the most expensive filter in this roundup, so it needs to earn its place on design.
Most of that design is aimed at the engineer. A one-way valve lets them add system chemicals, the body detaches completely for cleaning and there's an easy-access drain point. It captures magnetic and non-magnetic contaminants, goes under or over the boiler in 22 or 28 mm, and meets GASTEC standards according to Worcester.
The warranty is the weak spot. Worcester gives it 12 months, which looks short next to the three years Boilermag offers for far less money.
What we like
- Made in 22 and 28 mm versions
- Meets GASTEC standards according to Worcester
- Captures magnetic and non-magnetic contaminants
- Fully detachable body for cleaning
- One-way valve for adding system chemicals
- Fits under or over the boiler
What to know
- Most expensive filter in our roundup
- 12-month warranty is shorter than cheaper filters here
Our verdict
The Worcester Greenstar filter makes most sense alongside a Worcester boiler, or for anyone who wants a filter designed around easy servicing. It's dear for a 12-month warranty, though. The MagnaClean Professional 2 also comes in 28 mm for less, and the Altecnic Dirtmag IQ gives you sturdy construction at a lower price on 22 mm systems.
Best All-Rounder
Altecnic Dirtmag IQ Magnetic Sludge Filter
Best for: 22 mm systems that suffer with trapped air as well as sludge
Check Price On AmazonIf the radiators on your system keep needing bleeding, the Dirtmag IQ is the filter that helps with that. Its built-in air valve vents trapped air out of the system, while the filter captures both magnetic and non-magnetic dirt.
It's well built for the money too, a step up from most filters at its price, with a glass fibre polyamide 66 chamber, a high-density polyethylene internal filter and neodymium magnets. Altecnic gives it a triple separation action, it fits vertical or horizontal pipework, and Altecnic says it can be serviced without isolating it.
Pipe size is the one restriction, as it's only made for 22 mm. It comes with a two-year guarantee.
What we like
- Triple separation action
- Built-in air valve vents trapped air
- Glass fibre polyamide chamber with neodymium magnets
- Fits vertical or horizontal pipework
- Serviced without isolation according to Altecnic
- Two-year guarantee
What to know
- Only made for 22 mm pipework
Our verdict
Trapped air is the problem the Dirtmag IQ solves that most filters don't, thanks to its built-in air valve. Add the glass fibre chamber and neodymium magnets and it's a well-made filter for a 22 mm system without paying Worcester prices. On 28 mm pipework it won't fit, so look at the MagnaClean Professional 2 there.
Best Budget Runner-Up
Boiler-m8 Defender Magnetic Filter
Best for: The cheapest way to add a filter to a 22 or 28 mm system
Check Price On AmazonThe Boiler-m8 Defender is the cheapest filter in this roundup, and it works as a replacement for a tired filter as well as a new fit. It uses stainless steel filtration with high-powered magnets and removes both magnetic and non-magnetic debris.
It comes in 22 and 28 mm versions. The standard model has a manual air vent, and there's a version with an automatic vent if you'd rather not bleed it by hand. Boiler-m8 backs it with a two-year warranty and it's CE approved.
The instructions in the box are basic. An engineer won't need them, but anyone new to fitting filters will have to look up the details elsewhere.
What we like
- Cheapest filter in our roundup
- Made in 22 and 28 mm versions
- Stainless steel filtration with high-powered magnets
- Removes magnetic and non-magnetic debris
- Automatic air vent version available
- Two-year warranty and CE approval
What to know
- Instructions are basic and leave gaps for a first-time installer
Our verdict
The Boiler-m8 Defender gets a working filter onto your system for the least money, and it covers 28 mm pipework too. It's a practical pick when an engineer is fitting it during a service and won't need the basic instructions. For a longer warranty and more in the box, the Boilermag Domestic is worth the small step up.
What To Look For In A Magnetic Filter
Every filter on this list does the same basic job, so the right one for your boiler comes down to how it fits, how it's serviced and what's backing it. A few practical points decide which one suits your system.
Pipe Size And Fitting Position
The filter goes on the return pipe, the one carrying water back from the radiators, as close to the boiler as possible. Most domestic systems run 22 mm pipe at that point, but some larger systems use 28 mm, and only the MagnaClean, Worcester and Boiler-m8 filters here come in both sizes.
Space under the boiler matters as much as pipe size. Wall-hung combis in kitchen cupboards leave little room, so a compact body like the MagnaClean's, or a filter that fits at any angle like the Boilermag and TF1, saves the installer from rerouting pipework.
Magnetic And Non-Magnetic Debris
The black sludge in our TF1 photos is mostly iron oxide from the inside of steel radiators, and a magnet handles that well. Systems also carry sand, flux and scale that a magnet won't touch, which is why most filters add a mesh, cyclone or separation chamber. Most filters here also claim to catch non-magnetic debris, so compare the extras, such as an air vent or dosing point, as well.
A filter works best on a clean system. If the radiators are already cold at the bottom, the system needs a flush first, and our guide on draining a central heating system covers the first step.
How Easy It Is To Service
A filter only helps while it's being cleaned, so look at how the engineer gets the magnet out. Isolation valves, a drain point and a body that unscrews without tools all save time at the annual service. The TF1 cleans in place, while the Worcester filter has a fully detachable body.
Cleaning a filter loses a little water, so expect to top the boiler up afterwards. If the gauge keeps sinking after a service, our guide to a boiler losing pressure explains what to check.
Boiler Warranties And Filters
Some boiler manufacturers make a system filter a condition of their warranty, and Viessmann's advice on magnetic filters notes that skipping one can affect your cover. Check your boiler's warranty terms before a new install. The filter's own warranty varies a lot too, from 12 months on the Worcester to three years on the Boilermag.
Getting It Fitted
Fitting a filter means cutting into the heating pipework and draining part of the system, and on a gas boiler the work around it belongs with a Gas Safe registered engineer. The easiest time is during a boiler swap or annual service, when the system is already being worked on. Ask them to show you what the filter has caught each year, as it's the clearest sign of how your system is holding up.
Questions About Central Heating Filters
Are magnetic central heating filters worth it?
Yes, a magnetic central heating filter is worth fitting because it removes the iron sludge that clogs boilers, pumps and radiators. The TF1 on one of our rental boilers collected a thick coating of black sludge in a single year. Some boiler makers also make a filter a condition of their warranty, so it can protect your cover as well as the system.
Where should a magnetic filter be fitted?
A magnetic filter should be fitted on the return pipe, the pipe bringing water back from the radiators, as close to the boiler as possible. That way it catches debris just before it reaches the heat exchanger. Most filters fit under the boiler, and models like the Fernox TF1 and Boilermag Domestic can go on pipework at any angle.
When should a magnetic filter be cleaned?
A magnetic filter should be cleaned at least once a year, and the annual boiler service is the natural time to do it. The engineer isolates the filter, removes the magnet, wipes off the sludge and refits it, then tops up the inhibitor. A system with lots of sludge benefits from a check sooner after a new filter goes on.
Can I fit a magnetic filter myself?
A competent DIYer can fit a magnetic filter, since it's a plumbing job on the heating pipework rather than gas work. You'll need to drain part of the system, cut the pipe and refill and repressurise it afterwards. Check your boiler warranty first, as some require a registered engineer for work on the system, and we've always had ours fitted professionally.
Which central heating filter would you fit first?
The Adey MagnaClean Professional 2. We've had the earlier Professional on our own pipework without any complaints, and the updated version keeps a compact body that slots into the cramped space under a wall-hung boiler. It also comes in both 22 and 28 mm, so it suits more systems than the 22 mm-only filters here.
How much sludge does a magnetic filter actually catch?
Our service photos show it clearly. A Fernox TF1 Compact had been on the system for a year at one of our rentals, and its magnet came out caked in black sludge. Without the filter, that sludge would have been circulating through the boiler and radiators.
Is the Worcester Greenstar filter worth it without a Worcester boiler?
Only if easy servicing matters more to you than price. It's the most expensive filter in our roundup and carries just a 12-month warranty, so without a Worcester boiler to match it, the MagnaClean Professional 2 gives you the same 22 or 28 mm choice for less.
Is the Boilermag Domestic good enough for a rental property?
Yes, it's a sensible choice for a rental or a budget boiler swap. You get a three-year warranty and a well-stocked box at a lower price than the big names. Build quality is where the savings show, as it isn't up to the MagnaClean or Worcester units.
Our Choice Of Central Heating Filter
The Adey MagnaClean Professional 2 is the filter we'd have fitted first, with a compact body for tight spaces and a choice of 22 or 28 mm. The Fernox TF1 is the one to pick for awkward pipe runs, and our service photos show how much sludge its Compact sibling collected in a year.
For a tighter budget, the Boilermag Domestic gives you a three-year warranty and a full kit, while the Boiler-m8 Defender is the cheapest way to get a filter on the system.
Richard has spent years renovating properties and turning them into rentals and Airbnbs. Like a lot of people he started out as a beginner, and these days there isn't much DIY he won't take on.