In-line limescale inhibitor lifespan

How do permanent magnets fitted outside of a tube of water degrade over time?

The usual way that snake oil works :)

Assuming a combi boiler is this limescale Inhibitor fitted to the incoming water supply for hot water or is it fitted to the closed loop CH water?

It's fitted to the incoming water supply to the utility room which supplies the DHW, cold water supplies and top up to the CH.

They seem to be a requirement for a 10yr guarantee on a couple of major boiler suppliers.

I don't think permanent magnets are their sole mode of operation.

Could you kindly name and shame those brands, please?

One potential mode of operation is that people who have spent money on these devices are motivated to notice improvements that may not be there.

These are not particularly expensive. Google shows them on ebay for £12, which is small beer compared to the cost of a new boiler, so I wouldn't worry about it too much.

The magnetite filter seems to be a requirement by all major boiler manufactures for the 10 year guarantee. Also, it may also not be the best one on the market but must be a specific one recommended by the manufacturer.

Perhaps they fail when the limescale in the device builds up :)

Of course it has a 'lifetime guarantee'. When it ceases to work, it has expired and it's lifetime has come to an end. But it was OK before it wasn't OK IYSWIM, so up to the point when it expired, the guarantee was valid.

As to how they work, this, from here

So that explains it all, or not, ATCMB. The fact that calcium ions carry two charges not one (i.e. Ca++), and ions don't have a molecular structure (they're ions, not molecules) rather gives the game away as to the technical understanding of whoever wrote that explanation. In other words, they don't know and are attempting to blind the reader with science.

The question remains 'do these inhibitors actually work (which is highly suspect) and if so, how?'.

I believe they are. The theory is that it encourages a slightly different deposition of calcium carbonate that isn't hard and washes away

Calcium carbonate commonly crystallises in two forms - calcite and aragonite. They have different crystal structures. Calcite is the common form in for example chalk and limestone deposits, whereas aragonite is more commonly found in sea shells and corals. At a stretch I could believe that an applied magnetic field might cause aragonite to form rather than calcite (or vice versa), and that the consequence could be less lime-scale build-up.

Apparently this has been technically investigated, and it was concluded the magnetic treatment increased nucleation of aragonite and that only a thin brittle coating of lime-scale was formed instead of the usual hard scale. But why this should happen was not explained, at least not in the Abstract.

See

The following is as much as I can find:

from Instinct Pro Plumb & Heat Collection - Spring 2023by Marketing Sales

"Magnetic Scale Inhibitor The range of Instinct Scale Inhibitors are manufactured by Scalemaster® in the UK and incorporate the original Scalemaster® patented technology. Copper Mesh Enhances Limescale Inhibitor Performance Instinct and Scalemaster® in-line limescale inhibitors incorporate an active element (magnet or zinc anode) encased in pure copper mesh. The mesh increases the surface area of copper in contact with the water passing through the unit which enhances the electrochemical effect (removal of dissolved oxygen and treatment to prevent limescale precipitation). Only Scalemaster® products use this technology (Patent No.

Even if it is effective I don't see why it should still be effective over the lifetime of the boiler.

My error. Magentite filters are required by for instance on Worcester Bosch and Baxi but that is on the CH side not on the incoming for scale.

I think my installer thought that for the cost there was no penalty in fitting them. He's not one for making a "quick buck".

However I still cannot find anything to support they will last the lifetime (of the boiler to avoid any confusion of what is meant).

Patent description in a zip file here, for eg:

Assuming these lime scale inhibitors are strong permanent magnets, probably neodymium, whether an in-line fitting or clamped on the outside of the rising main, I see no reason why they shouldn't last for a very long time, much like any other permanent magnet.

I imagine it should be possible to make your own, with a couple of magnets recovered from a scrap HDD and some duck tape to hold it onto the rising main.

It's just a magnet. What would be the failure mode of the magnet in your installation?

The magnetic filters collect a lot of black crud, that would otherwise be floating around the system and clogging up the heat exchanger. So, I understand why the boiler manufacturers recommend them so strongly.

As I said, for £12 or so, it's not a catastrophe.

The magnets will last pretty much forever - certainly the full life of the boiler. It has no moving parts. So, whether it does anything useful or not, I'd expect it to work exactly the same in 10 or 20 years time as it does now.