SandCould you explain which particles you would expect to find (in a heating system) that are not attracted to a magnet?Its a very powerful magnet and will strongly attract magnetic particles.
The only problem is that they do not attract non-magnetic dirt.
Wood
Bits of solder
Copper (shavings)
Alluminium
Brass
Limescale
Red/brown ferrous oxide
Plastic
Maybe you are not the boiler expert you pretend to be goldborg?
How many have you installed?
Or repaired?
And how many of those were done legally?