What a magnetic filter does
It catches the tiny bits of magnetite (that black sludge) and metal debris circulating in the system, before it ends up inside your new boiler’s heat exchanger, pump, or valves.
Magnetic filter & inhibitor for a new boiler
Not an “extra” — it’s protection.
If you’ve ever sat through a boiler quote and heard “filter and inhibitor” said like it’s an upsell… I get why people switch off. The problem is: in London, system water is rarely perfect. A brand-new boiler dropped onto a tired system without protection is basically a new engine filled with old grit.
We’re ARA Services Ltd — Gas Safe engineers based in Forest Gate (E7). We’re in and out of Stratford, Leyton, Hackney, Islington and the wider North/East patch most weeks. If you want a straight answer on what your system needs, call +44 7727 154 746. Phone first. No finance plans. No nonsense.
Worcester • Vaillant • Ideal
Warranty-friendly installs
London system-water reality
What inhibitor does
It’s a chemical treatment added to the system water that helps reduce corrosion, sludge build-up and scale. In normal language: it helps keep the water “well-behaved”.
If your radiators have ever had cold spots, if the old boiler was noisy, or if the system water looks dark when bled,
protection is almost always a smart move. It’s cheaper than repeat callouts and it helps keep warranties clean.
If you’re also weighing up whether the system needs cleaning first, don’t guess:
power flush vs chemical clean (when it’s actually needed).
Why this matters more in London than people realise
London’s housing stock is mixed: terraces with old pipework, conversions where the heating has been “modified” five times, flats where the system gets topped up without anyone checking inhibitor levels, and radiators that have been on and off the wall during refurb jobs. All of that creates debris.
When a new boiler goes in, it runs differently too — higher efficiency, different flow characteristics, tighter waterways in modern heat exchangers. That’s great… until sludge and metal bits start circulating and you get restrictions, noise, pump issues or sensor faults.
“Black water” is common
Bleed a radiator in a lot of London homes and you’ll see it: water that’s grey, brown, sometimes basically Guinness. That’s magnetite and corrosion products. A magnetic filter is built for that exact reality.
New boilers aren’t as forgiving
Old boilers used to tolerate a bit of muck because they were chunky. Newer ones are more efficient and more precise — which means small restrictions can cause bigger headaches.
For the wider “installed properly” picture, start here: boiler installation done properly.
Warranty + paperwork reality
Manufacturers want the system protected and commissioned properly. That usually means clean-enough system water, inhibitor, and sensible protection. If it’s skipped and faults follow, it’s not unusual for warranty conversations to get… awkward.
If you’re choosing between brands: Worcester vs Vaillant vs Ideal.
A quick story: the “new boiler, still noisy radiators” callout
We got called to a place near Leyton where a boiler had been swapped recently by another firm. The customer’s words were basically: “It’s new… so why does it sound like a kettle in the pipes?”
Boiler was fine. The system wasn’t. No magnetic filter. Inhibitor wasn’t topped up properly. Radiators had years of sludge. The pump was working harder than it needed to and the flow was messy. Once we cleaned what needed cleaning and added proper protection, it calmed right down.
That’s why we don’t treat filters and inhibitor like optional extras. They’re the boring stuff that stops a “new boiler” turning into repeat callouts.
If your quote is cheap and it doesn’t clearly mention protection/commissioning,
it’s worth reading:
why cheap boiler quotes fall apart.
When you genuinely need a magnetic filter + inhibitor
Very common “yes” situations
- Radiators cold at the bottom / uneven heating
- Old boiler had frequent faults or made banging/rumbling noises
- System has been topped up a lot (fresh water brings oxygen → corrosion)
- Older pipework, older radiators, conversions, extensions
- You’re installing a modern combi with tighter waterways
When it might feel like “less of a thing”
Brand-new system, new pipework, new radiators, properly cleaned on install, and treated from day one — that’s the dream scenario. In those cases, the filter still helps, but you’re not fighting years of muck.
If you’re unsure, you can send photos and we’ll give a straight steer: message the setup here.
What happens if you skip it
- Debris can restrict the heat exchanger
- Pumps and valves work harder (wear + noise)
- More chance of sensor/flow-related faults
- Radiators stay uneven and you chase the thermostat
- Warranty conversations can get complicated if protection is missing
Important: a magnetic filter is not a “magic fix” for a filthy system.
If the system is heavily contaminated, cleaning comes first (or alongside), then protection.
That’s why we keep this separate:
do I need a power flush with a new boiler?
How we fit and maintain protection (so it actually works)
The protection only works if it’s installed sensibly and maintained. A filter needs to be accessible, and it needs to be cleaned periodically (especially after installation / cleaning work). Inhibitor needs to be dosed correctly and checked when the system is drained or topped up.
Filter placement that makes sense
We position it so it’s doing its job and can actually be serviced. We’ve seen filters installed where you basically need yoga training to open them. Looks neat… until someone needs to clean it.
Commissioning and handover
On install day we explain what’s been fitted, why it matters, and what to watch for. You’re not left with a shiny boiler and zero clue.
If you’re planning the full install route, this is the hub: boiler installation in London.
Real-world maintenance note
If you drain radiators, swap valves, or have plumbing work that empties part of the system, inhibitor levels can change. Tell your engineer. It’s a small thing that prevents bigger problems.
If something’s already acting up, start with diagnosis: boiler repairs & fault finding.
Not sure what your system needs? Quick phone check.
Call +44 7727 154 746. If you’re in a terrace near Wanstead Flats, a flat around Stratford, or anywhere in North/East and you’ve got 2 minutes, tell us: boiler type now, radiator condition (cold spots or not), and whether you’ve been topping up pressure. We’ll tell you if protection is “must-have” or “nice-to-have”.
Call — quick honest advice
Prefer photos? Use: our contact form (boiler area + a radiator bleed point if you can).
What people mention in reviews (the pattern)
Customers don’t ask for “the most technical install”. They want: clear explanations, honest quoting, and the job left tidy. That’s the stuff that keeps coming up.
“Worked without taking a break… fitted a new boiler and cleaned up when they finished.”
Alison Louis“Identified the issues immediately and fixed the problem. Very professional.”
Rachel Boston“Punctual, professional, and true to their quote — highly recommended.”
Elimelech Halberstam
If you’re reading this because you’re trying to avoid future breakdowns, the biggest wins are usually:
protection (filter + inhibitor), correct commissioning, and not oversizing the boiler.
Boiler sizing guide:
choose the right boiler size.
FAQ (different angles, not copy-paste)
Is a magnetic filter really necessary on a new boiler?
In a lot of London systems, yes — because the debris already exists in the radiators and pipework. A filter is there to catch it before it ends up inside the new boiler. If your system water is clean and the system is new, it’s less critical, but still a good layer of protection.
What does inhibitor actually do — and can it “fix” sludge?
Inhibitor helps slow corrosion and reduces new sludge forming. It doesn’t magically remove years of existing contamination. If the system is dirty, cleaning is the fix, then inhibitor helps keep it that way. This is the detailed guide: power flush vs chemical clean.
Will skipping protection cause breakdowns?
Not instantly every time — but it increases the risk. Debris can restrict flow, stress pumps and valves, and cause nuisance faults. You might be “fine” for a while, then you’re calling someone out in January.
Does it affect Worcester/Vaillant/Ideal warranties?
Manufacturers expect correct installation and commissioning, and they generally want system protection and correct water treatment. Every warranty situation is case-by-case, but skipping protection can make any warranty conversation harder than it needs to be.
How often does a magnetic filter need cleaning?
It depends on the system condition — a recently cleaned or new system may be low-maintenance, while an older system can load up quickly. After an install or cleaning work, it’s common to check it because it’s doing its job (catching debris). If you’re unsure, ask during servicing.
Can I tell if my system water is bad without being an engineer?
A few clues: radiators cold at the bottom, frequent topping up, noisy circulation, black water when bleeding a radiator, and slow heat-up. If you want a quick sanity check, send a couple of photos and a short note via our message form or call +44 7727 154 746.