Domakihub How to Fit a Magnetic Boiler Filter and Keep Sludge Out
Protect your boiler and radiators from magnetite sludge with one straightforward DIY installation.
Reviewed by Domakihub home & decor pros · 2026-06-23 · 5 min read
A magnetic boiler filter is one of the most cost-effective ways to extend the life of a central heating system — whether you manage a family home in Athens, a holiday villa in Crete, or a boutique hotel on the islands. Left unchecked, black magnetite sludge silently clogs radiators, corrodes heat exchangers, and can void boiler warranties. The video above walks through a Magnaclean installation in real time; the steps below give you the full picture so you can carry out the job confidently or brief a plumber before they arrive.
Why Magnetite Sludge Is Such a Problem
When steel radiators and iron pipework are in contact with water and oxygen, they corrode and release tiny iron-oxide particles. These particles are magnetic, which is exactly what a magnetic filter exploits — a powerful rare-earth magnet grabs the particles out of circulation before they can settle inside the boiler heat exchanger or block radiator valves.
In Greece's hard-water regions this process is accelerated because limescale and corrosion by-products combine, thickening the sludge faster than in softer-water areas. Properties left unoccupied for part of the year — typical of holiday lets — are especially vulnerable because the system stagnates and oxygen levels spike when heating is off.
Choosing the Right Filter for Your System
Magnetic filters are rated by connection size, most commonly 22 mm (standard UK-style pipework also common in Greek installations) or 28 mm for higher-flow systems. The two dominant brands are ADEY MagnaClean and Sentinel, but several own-label versions offer the same rare-earth magnet core at lower cost. For a typical apartment or villa with six to twelve radiators, a 22 mm Professional-grade unit is sufficient.
Position matters: the filter must go on the return pipe as close to the boiler as possible, so that sludge-laden water passes through the magnet before it re-enters the heat exchanger. Confirm the pipe is the return by feeling it when the heating is running — the return pipe is noticeably cooler than the flow pipe.
How to Fit a Magnetic Boiler Filter: 5 Steps
- 1
Turn off the boiler and isolate the circuit
Switch the boiler off at the programmer and let the system cool for at least 30 minutes. Close the service valves either side of where you plan to fit the filter. If there are no local service valves, close the main system fill valve and drain a few litres from the lowest drain cock to reduce pressure before cutting the pipe.
- 2
Cut the return pipe and fit compression tee fittings
Mark and cut a section of the return pipe long enough to accept the filter body plus two tee connectors (typically 100–120 mm). Deburr the cut ends with a pipe reamer or fine emery cloth. Slide compression nuts and olives onto each pipe end before pushing on the tee fittings; tighten each nut one full turn past hand-tight using an adjustable spanner. Do not overtighten or you risk cracking the olive.
- 3
Mount the filter body and make the connections
Thread the filter body into the tee fittings — most units use BSP threaded ports (1 inch or ¾ inch) with a fibre washer seal. Apply PTFE tape to male threads (five to seven wraps, clockwise). Hand-tighten first, then snug with a spanner — a quarter turn past the point of resistance is usually enough. Hang the filter body using the supplied bracket if the pipe run is horizontal, to avoid strain on the joints.
- 4
Refill, bleed, and check for leaks
Slowly reopen the isolation valves and allow the system to refill. Open the boiler's filling loop briefly if pressure has dropped below 1 bar (check the gauge on the boiler front panel). Bleed any radiators that show air, starting from the ground floor and working upward. Run the boiler on a test cycle and inspect every joint on the new filter for seepage — wipe joints dry first so even a slow drip is visible.
- 5
Flush after the first 30 days, then annually
After the initial month of operation, switch off and isolate the filter, unscrew the collector cap at the bottom, and slide out the magnet rod. You will likely see a dark slurry clinging to it — this is magnetite that would otherwise have entered your boiler. Wipe the magnet clean with a cloth, rinse the housing under a tap, and reassemble. Repeat this service every twelve months or whenever boiler efficiency drops noticeably.
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FAQ
- Can I fit a magnetic filter myself, or do I need a licensed plumber?
- In Greece, work on the boiler itself must be carried out by a licensed gas engineer, but fitting a magnetic filter on the pipework external to the boiler is generally DIY-permissible. That said, if your boiler warranty requires a certified annual service, ask your engineer to fit and log the filter at that visit so the paperwork stays clean.
- Which pipe should the filter go on — flow or return?
- Always the return pipe. Water returns from the radiators carrying the highest concentration of sludge particles. Intercepting them on the return means the magnet captures them before they re-enter the boiler's heat exchanger, which is where damage is most costly.
- How do I know if my heating system already has too much sludge to benefit from a filter alone?
- If multiple radiators have cold spots at the bottom, the boiler makes a kettling or banging noise, or your energy bills have risen without explanation, the system likely needs a full power flush first. A power flush circulates a descaling and corrosion-inhibitor solution at high velocity to shift compacted sludge. Fit the magnetic filter immediately after flushing to prevent sludge from rebuilding.