Magnetic Filters for Central Heating in London: Magnaclean, Fernox TF1, and How They Work

What a Magnetic Filter Does

A magnetic filter — also called an inline magnetic filter or system filter — is a device fitted in the pipework on the return pipe to the boiler. Inside the filter housing sits a powerful neodymium magnet. As heating water circulates through the filter housing, magnetite particles (iron oxide, which is magnetic) are attracted to the magnet and held against it rather than continuing to circulate through the system. The magnet effectively strips magnetite out of the water before it reaches the boiler heat exchanger and the circulator pump.

The filter is cleaned periodically — typically at the annual boiler service — by removing the cap, withdrawing the magnet cartridge, and wiping off the accumulated black sludge before replacing. The quantity and consistency of the sludge collected at each service is a useful indicator of system condition. A system that has been adequately inhibited and does not have significant corrosion will yield a small amount of fine black residue. A poorly inhibited or corroded system will yield a large quantity of thick black sludge at each service.

Magnaclean

The Adey Magnaclean is the most widely recognised magnetic filter brand in the UK central heating market. It comes in several sizes — the Magnaclean Professional 2 (22 mm) is the standard for domestic London central heating systems. The filter housing is red, compact, and fits inline on the 22 mm return pipe to the boiler. Cleaning involves removing the bottom cap and swiping off the sludge from the magnet cartridge — a two-minute task with no tools. The Magnaclean Professional 2 has an integral isolation valve on both sides of the housing, allowing the filter to be isolated for cleaning without draining the system. Adey also produces a combination magnetic and mesh filter (the Magnaclean Duo) that captures both magnetic and non-magnetic debris.

Fernox TF1

The Fernox TF1 (Total Filter) is the other major brand in the UK domestic market. It is available in a Compact version for space-constrained installations and a standard version with greater sludge capacity. The TF1 uses a different magnetic arrangement from the Magnaclean but achieves equivalent capture efficiency. Fernox produces a combined filter and chemical dosing device (the TF1 Omega) that allows system inhibitor to be added directly through the filter housing.

When to Fit a Magnetic Filter

A magnetic filter should be fitted at new boiler installation — this is specified by boiler manufacturers (Worcester Bosch, Vaillant, Ideal, Baxi) as a requirement for full warranty compliance, and many Gas Safe engineers will fit a filter as standard when installing a new boiler. If a filter is not fitted at new installation, it should be fitted at the first annual service.

For existing London systems without a filter, the most impactful time to fit one is at a pump replacement (because pump seizure is caused by sludge — fitting a filter at the same visit prevents the new pump from suffering the same fate) or at a boiler repair for a heat exchanger fault (same logic). Fitting a filter to a heavily sludged system without first powerflushing means the filter captures sludge already in circulation but does not remove sludge already deposited in radiators and pipes — a powerflush is the correct first step.

Filter Cleaning Frequency

Manufacturer guidance for most domestic magnetic filters is annual cleaning — typically at the annual boiler service. In practice, a new filter fitted to an un-powerflushed London system will fill with sludge rapidly in the first few months. It is worth checking the filter at three months post-installation on an older system to assess sludge levels and clean if necessary. Once the circulating sludge is captured and the system is inhibited, subsequent annual cleans should yield much smaller quantities. Prestige Engineers fit Magnaclean and Fernox TF1 filters across all London boroughs from £150 supply and fit.