Magnetic filter vs inline strainer for heating systems
A magnetic filter captures iron oxide sludge circulating in the heating water using a strong magnet, and is cleaned by opening a valve and rinsing the collected debris out. An inline strainer catches larger solid debris, such as jointing compound or swarf, with a mesh screen and suits protecting a specific component like a pump.
A magnetic filter and an inline strainer explained in plain terms
Magnetic filters are now specified by most boiler manufacturers as a condition of the extended warranty, because magnetite sludge is the leading cause of pump, valve and heat exchanger wear. Strainers are more commonly used where a particular sensitive component, such as a plate heat exchanger or a new pump, needs protecting from coarse debris during and shortly after installation work. The two are not interchangeable for warranty purposes.
Relevant registrations
- Gas Safe registered for domestic gas boiler work
- OFTEC registered for oil boiler work
- Worcester Bosch Accredited Installer
A magnetic filter and an inline strainer: engineer's shortlist
- Manufacturers commonly require a magnetic filter for warranty validity
- Strainers catch coarse debris a magnet cannot
- Magnetic filters need periodic cleaning as part of a service
- Strainers can restrict flow if not cleaned after new pipework
- Both are fitted into the return pipework near the boiler
Questions we get asked
- Can I have both fitted?
- Yes, they protect against different debris types and are sometimes combined on heavily sludged systems.
- How often should a magnetic filter be cleaned?
- At every annual service as standard, and sooner if the system has recently been flushed or worked on.
Related help pages
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- Older system layoutsVented gravity-fed systems: how older heating layouts work
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Where we deal with this
Book a visit for a magnetic filter and an inline strainer
In practice: A magnetic filter protects long-term system health; a strainer protects specific components during and after works.
For gas work, use a Gas Safe registered engineer; for oil work, use an OFTEC-registered technician.
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