On Fri, 30 Oct 2009 15:41:56 +0000, Ash wrote:

My mother telephoned today to say that the heating engineer had called to
identify her hot water problem with her combi and they had told her that her
Heat Exchanger had furred. I haven't the make or model number for the combi
but I don't think it really matters as most combi work on a similar
principle (?) that they heat hot water for the central heating/radiators on
one system and the heating of the hot water is a separate system and both
systems are contained within the combi.

No, the type you describe was always relatively uncommon and AFAIK no-one
makes that type any more (i.e. as high-efficiency/condensing boilers).
Much more common is the arrangement whereby the primary gas-water heat
exchanger heats water that goes either to the central heating or to a
secondary heat exchanger that heats the hot water. These secondary heat
exchangers are usually plate types (PHEs) and these are susceptible to
scaling ('furring') up on the secondary, domestic hot water, side, or to
getting blocked up with gritty magnetic debris on the primary side from
the water that also goes round the radiators. In my limited experience of
this phenomenon it seems to be Baxi Combi 80 or 100s and Potterton
Performas (same model, different badge) which are susceptible.



The query my mother has raised is that the heating engineer has said that
she needs a Magnaclean filter fitting to stop the hot water heat exchanger
furring up again.

Sounds like a good idea. However I fitted a Fernox Boiler Buddy (similar
idea - magnetic filter) to one of my victim machines and its PHE still got
blocked! A quick swish round the system with the powerflushing machine
bought several months' trouble-free operation but the problem eventually
recurred. Fortunately with these boilers one can swap the PHEs in a matter
of a few minutes, and Norstrom (who make my flushing machine) do an
adaptor specifically for power-flushing these PHEs (I wonder what that
tells us about them!). So now I keep a cleaned one in the van and swap it
for the one in each latest victim boiler as I come across them!


If she doesn't have one fitted then, whilst they'll
fix the heat exchanger with a sonic cleanse this time,

Interested to know what a 'sonic cleanse' is.

... To
me the requirement to fit a Magnaclean, whilst good advice for the
central heating/radiators, has nothing to do with the fault and smacks
of sharp sales practice and someone wanting to boost their sales bonus.

I think Magnaclean-type devices aren't for protecting radiators so much as
protecting the narrow waterways in boilers' heat exchangers - including
the primary gas-water heat exchangers in modern boilers.

Any thoughts?

I think your mother's engineers may be making an honest and sensible
attempt to deal with a problem not just immediately but in the long term.


--
John Stumbles -- http://yaph.co.uk

Many hands make light work. Too many cooks spoil the broth.