Magnet Jacket for Fernox TF1 Sigma HP filter

Motivation

At some point, I realised that my pre-plumbed cylinder for the Mitsubishi Ecodan heat pump comes with a Fernox TF1 Sigma HP debris filter which is so “innovative” that it completely lacks basic magnetic filtration for rust and other ferrous particles. As a result, my fine strainer filter (200 micron) gradually reduced the flow rate until it became completely blocked.

Initially, I considered swapping it for a Fernox TF1 Sigma (non-HP) version, which includes a removable magnetic core. Unfortunately, that model has significantly higher flow resistance: the maximum flow is limited to 50 L/min, compared to 80 L/min for the HP version.

To avoid sacrificing flow performance, I decided to design a non-invasive magnetic jacket for the existing filter, allowing me to combine high throughput with effective magnetic filtration.

Parts required for assembly

• Disc magnets 15 × 5 mm — 18 pcs
  I used N42 magnets: slightly cheaper and with a lower risk of buying fake N52s.

• M3 × 12 hex head cap screw — 1 pc

• M3 nyloc nut — 1 pc

The filter body can get quite warm during the DHW cycle (depending on system settings), so I chose ASA or ASA-CF for printing. Print tolerances may vary; if the fit feels slightly loose when tightened, wrapping the top part of the filter body with one layer of electrical tape works well to improve the grip.