Magnetic Filter Installation London

What is a magnetic filter?

A central heating magnetic filter is a sealed unit fitted into the heating pipework — usually on the return pipe just before the water re-enters the boiler. Inside is a strong magnet. As water flows past, magnetic particles such as magnetite are pulled out of the flow and held on the magnet.

Many filters also have a separate chamber that slows the water down so heavier non-magnetic debris can settle out. When the filter is serviced, the magnet is removed and the collected debris is flushed away.

How a filter protects your boiler

The boiler’s heat exchanger and pump are the parts most vulnerable to debris. Placing the filter on the return, before the boiler, means water is cleaned just before it reaches those components. Over time, a filter captures a surprising amount of material — you can see it when the magnet is taken out.

What a magnetic filter can’t do

It’s important to be realistic. A filter only captures debris that is circulating. It won’t remove sludge that has already settled in the bottom of radiators, and it doesn’t stop corrosion. That’s why, on a contaminated system, the sequence we recommend is:

1. Clean — remove existing sludge with a power flush.
2. Protect — add inhibitor at the correct concentration.
3. Filter — fit a magnetic filter to catch what forms from then on.
4. Maintain — clean the filter and test the inhibitor at each annual service.

Why inhibitor is so important

A central heating inhibitor is a chemical treatment added to the system water that helps slow corrosion and scale formation on the metal surfaces inside. Less corrosion means less magnetite, less sludge and less gas in the radiators.

Inhibitor gets diluted over time — every time the system is topped up, drained for a repair, or loses water through a leak. Its level should be checked, typically once a year, and topped up if needed. BS 7593 includes checking system water quality as part of ongoing maintenance.

Magnetic filter after a power flush

After a power flush, your system is as clean as it’s likely to be. Fitting a filter at that point means it starts working on clean water and can catch the small amount of new debris that continues to form, rather than being overwhelmed. For a new boiler, a filter is also frequently part of the manufacturer’s warranty requirements — see power flush before a new boiler.

Choosing and fitting a filter

We fit filters from established manufacturers, sized to your pipework (typically 22mm or 28mm). Positioning matters: the filter needs to be accessible for servicing and fitted in the right place relative to the boiler. We’ll explain the options and include the price clearly in your quote.