In an earlier contribution to this discussion,
Hugo Nebula abuse@localhost wrote:

On Sun, 18 Sep 2005 12:04:59 +0100, a particular chimpanzee named "Set
Square" randomly hit the keyboard and produced:

Apportionment of blame could be a bit of a challenge - because the
boiler manufacturer and installer will blame each other. Start with
the installer - the black water has *got* to be down to him due
either to:
* insufficient flushing
* not putting inhibitor in, or
* incorrect system design

or some combination of these.

It seems the first and third are definitely there. Crawling round the
loft space yesterday, I found an empty 1 litre bottle of Sentinel (?)
inhibitor. Assuming they put the full bottle in and no more, is this
enough for a seven radiator system?

That should be enough - unless, of course, it has somehow got diluted. This
can easily happen if the water level is too high in the F&E tank. When the
system heats up, the water expands and runs out of the overflow. When it
cools down, the level drops - and fresh water comes in through the ball
valve. Or there could be an undetected leak somewhere - maybe under the
downstairs floorboards? - again with automatic topping up with fresh
oxygenated uninhibited(!) water.

Have you examined the boiler yourself to verify the plumber's diagnosis? Is
there any chance that there's just a leaking joint rather than a corroded
heat exchanger? The heat exchanger is probably in several bits which bolt
together - with gaskets to seal the joints. Unless there were a serious
manufacturing defect, it seems more likely to me that a gasket has failed
than that the metal has corroded through.
--
Cheers,
Set Square
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