How to judge when CH pipe restricted by iron oxide - magnet test?

[pennine_lad]

Hi

Have a mid 80s build CH system in soft water area. About 15 years ago a CH section of pipe in immersion cupboard above the pump where believe gets hottest was identified as part blocked by the heating engineer with magnet. Removed and cleaned out as bore reduced considerably.

A very strong magnet again sits under its own weight on this part of the pipe (marked with red spot in image), the entire H section either side of cross piece holds the magnet, especially at cross piece. Asked British Gas engineer when round to annual service the boiler and remarked not normally removed but would use a powerflush. But gently expressed my doubt as if would clear the hard deposits which last time needed scraping off.

How reliable is the magnet test to judge if the section needs replacing or cleaning. The boiler seems to cycle well on the water heating cycle but does audibly kettle on the CH circuit (Glow-worm 18hxi boiler set at 63C). Can this sort of deposit be removed by adding one of the proprietary chemical flushes.

There has been installed for some years a Spirotech magnetic filter which if take a sample there's a light fine black deposit after a year.

Thanks for any insight.

David

 

[Exedon]

As that magnet is staying put there must be a fair build up of ferrous crap.
We would just drain cut pipework and repipe, at least then you're certain you have cleared pipework

 

[JohnD]

I have a Spiro, and find it is nowhere near as good as a Magnaclean at collecting circulating particles.

Your blockage is probably too hard for a chemical clean to shift it, but you could give it a try, as cost and effort are small.

I understood that the hard blockages are where the iron oxide combines with limescale, but you say you are in a soft water area. When you cut out the pipe, scrape the deposit and see how hard it is.

If you have a feed and expansion tank, bale it out and shovel away the mud before you start work, so it doesn't wash down into the pipes.