Magnetic System Filters and Keeping Sludge Out of the Boiler
A magnetic filter sits on the heating circuit, usually near the boiler, and captures the black iron oxide sludge that builds up in radiators and pipework over years.
A magnetic filter sits on the heating circuit, usually near the boiler, and captures the black iron oxide sludge that builds up in radiators and pipework over years. It protects the boiler's pump and heat exchanger, but it needs periodic cleaning out to keep doing its job.
What it does
A magnet inside the filter body attracts and holds magnetite sludge as system water passes through, stopping it reaching the boiler's narrower internal waterways.
How it fails
It doesn't fail so much as fill up — if never cleaned, it stops capturing new debris effectively and can itself restrict flow once heavily loaded.
Repair or replace
Filters are cleaned out rather than replaced in almost all cases, usually as part of an annual service, unless the body itself is physically damaged.
Why we recommend one on every boiler replacement
- Protects the new heat exchanger from years of accumulated sludge
- Makes future servicing quicker to assess system condition
- Reduces noisy circulation caused by debris
- Straightforward to clean out during an annual visit
Who does the work
- Gas Safe registered engineers — registration 554328
- Worcester Bosch accredited installer
- John The Plumb Ltd, company registration 10026483
Add or service a magnetic filter
Tell us whether you already have a filter fitted and when it was last cleaned, and we'll advise what's worth doing at your next service.
Questions we get asked
Is a magnetic filter compulsory?
It's widely recommended manufacturer good practice on new boiler installations, though requirements vary by manufacturer and we'll confirm what applies to your boiler.
How often does it need cleaning?
Typically checked and cleaned at each annual service, though a system with a lot of old sludge may need it more often initially.
Will a filter fix an already sludged-up system?
It captures ongoing debris but won't clear existing sludge from radiators — a powerflush addresses that separately.