Fernox TF1 Sigma Mini review

Name: Fernox TF1 Sigma Mini 22mm Slipsocket
Brand: Fernox

Fernox TF1 Sigma Mini 22mm Slipsocket

By Tom Calder

Key specs

The maker's figures.

What it is: Compact neodymium magnetic system filter
How it works: High-powered neodymium magnet
Fits: 22mm slipsocket connection
Install effort: Fitted into the sealed heating system

Our verdict · Researched

4.2 / 5

A well-made, compact neodymium magnetic filter that protects the boiler's heat exchanger from magnetite sludge, which is the main cause of banging noises, cold spots on radiators and gradually worsening efficiency. Fitting it means cutting into a sealed heating system, so treat this as a competent-DIY-or-plumber job, and get the inhibitor topped up afterwards in line with BS 7593:2019.

Best for: Combi or system boilers with a tight service cupboard, where a full-size in-line filter simply won't fit.
Skip it if: You've got normal clearance under your boiler

Price

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Researched, not used. We haven't used this product. This review is built from the maker's specifications, owner reports and our own sizing.

What we like

Genuinely compact — Fernox states as little as 105mm clearance needed, so it fits under boilers and in cupboards a standard filter can't
High-powered neodymium magnet housed in a withdrawable dry pocket, so servicing via the drain point is quick and mess-free with no disassembly needed
Established UK brand (Fernox invented the in-line magnetic filter category) with a 10-year warranty

Worth knowing

Noticeably pricier than the standard full-size TF1 Sigma for the same core filtration, so only worth the premium if space is genuinely tight
Installation involves draining and cutting into the sealed system — not a first-time DIY job

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Who shouldn't buy this

Skip it if you've got normal clearance under your boiler — the standard-size TF1 Sigma costs less, is just as easy to service, and gives the same magnetic protection.

How this review works

This is a Researched review: we haven't used this product. We check every specification against at least two independent sources, re-check the UK price on a schedule where we can track it automatically, and say plainly who it isn't for. Commissions never change a rating.

How we review →Full methodology →

If this isn’t the one

Adey MagnaClean Professional2 Filter & Chemical Pack 22mm — CP10300625

4.4

Best for Homeowners protecting a working boiler and radiators from sludge build-up, fitted as part of a proper service or after a flush.

£119.99Check price at Amazon →

in stock when checked

as of 5 Nov 2026, 22:07 GMT · Details

Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon.co.uk at the time of purchase will apply to the purchase of this product.

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