Magnetic filter or permanent treatment: what each one actually does

Both units fit in the same place, on the circuit return before the boiler, and both are sold on the same promise: a clean circuit. But they tackle the problem at different moments. A magnetic filter captures the ferrous particles already circulating in the water. Permanent physical treatment acts on those particles' ability to adhere, and includes a curative effect on what is already deposited on the walls.

Put plainly: one collects, the other stops things sticking and lifts what has stuck. They are not exact substitutes, and understanding the difference avoids buying the same function twice or leaving the problem half solved.

What a magnetic filter does, and where its limit lies

A magnetic filter is a canister fitted on the return with a powerful magnet inside. The water slows on entry, the heavier particles settle out and the ferrous ones are trapped by the magnetic field. At each service the canister is emptied and the accumulated matter removed.

It is a useful and well-executed device. Its limits are three, and all of them matter when deciding:

1. It does not stop sludge forming. It captures what has already formed and is already circulating. Corrosion keeps producing magnetite at the same rate.
2. It does not act on what is stuck. Deposit fixed to the bottom of a radiator or coating the inside of a heat exchanger does not circulate, so it never reaches the filter.
3. It depends on someone emptying it. A saturated filter stops retaining and adds pressure drop into the bargain. In installations without a maintenance contract, it is common for one to go years without being opened.

What permanent physical treatment does

The DS-i acts on the fluid as it passes, by the same physical route as the limescale unit: vortex, Venturi acceleration and low-frequency sonicophysical waves. The result is that suspended particles end up in a state where they do not adhere to pipe walls or to circuit components. New deposit stops forming. And those same waves progressively break up the deposit already there, which comes away gradually and is flushed out at purges.

The release is gradual by design, not by weakness: the aim is for deposits to come away as fine particles rather than as plates capable of blocking a thermostatic valve or a heat exchanger downstream. On a badly degraded circuit the process can take several months.

The unit consumes nothing: no electricity, no water, no consumables. The circuit's own hydraulic energy drives the internal mechanism.

Retaining or preventing adhesion: why they are not the same

The distinction looks subtle and it decides the outcome. A filter works downstream of the problem: it waits for the particle to exist, come loose and pass through its body. Permanent treatment works on the condition that makes the particle stick, so it acts across the whole circuit at once, including the areas where water moves slowly and from which nothing would ever be carried to the filter.

What about chemical flushing? And inhibitors?

A chemical flush is a one-off curative operation: drain, circulate a descaling and dispersing product, rinse and refill. It leaves the circuit clean that day and it is the best way to start from zero when the condition is very poor. It prevents nothing: without a permanent measure behind it, the circuit returns to where it started.

A corrosion inhibitor is genuinely preventive, but it only works while the concentration holds. Every partial drain-down, every top-up and every intervention dilutes it, so it demands periodic checking and redosing. It also creates a dependency on a product which, in industrial installations, becomes a cost line and a waste management issue.

Does it make sense to fit both?

Yes, in two specific situations. First, on a badly degraded circuit during the cleaning phase: while the DS-i lifts the accumulated deposit, a magnetic filter collects part of that material and reduces how often purging is needed. Second, on large installations where the volume of material released during the first months justifies a capture point.

On a domestic installation in good condition, fitting both is redundant. The sensible sequence is a chemical flush if needed, permanent treatment after, and a magnetic filter only if the case calls for it.

DS-i range by size

The unit is fitted on the return, before the boiler or generator, with straight pipe before and after and with no welding on the body. Installation detail and the symptoms that justify intervening are in Sludge in closed circuits.