In article .com,
"Neil" writes:
Thanks again.

Apparently the reason for replacing a part rather than cleaning it was
down to the legality of having to dispose of the chemicals afterwards
in the right way.

The plumber was telling you a lie. The chemical is eactly the
same as you use to descale your kettle, and you do the same with
it when you've finished.

I just looked at the pipes the chap said to cut and place the pump on -
the mains water inlet and the HW outlet. Would that still have no
effect as you mention above?

Oh, that might work, but I never heard of anyone cleaning a plate
exchanger that way. Anyway, you should really clean both sides.
The other side won't be scaled up, but it might well have debris
from the heating system in it which can be washed out.
Oh, and what was he suggesting you should do with the cleaning
chemicals afterwards? ;-)

I suspect your plumber doesn't know what he's doing or is just
plain dishonest, but it would be interesting to see if any of the
plumbers/heating engineers in this newsgroup think this is a
standard way to clean a plate exchanger.

To be honest I'm desperate to perform what you did and remove the part
but I admit my plumbing is basic. Is it a case of 'unscrew this, remove
part, unclip that' etc. or were there situations where specialist
knowledge/tools or experience is needed? The engineer mentioned the
tricky bit is normally putting the heat exchanger back in.

Look at the boiler servicing instructions. It will tell you how to
remove and replace the plate exchanger (secondary heat exchanger).
IIRC, it is held in by just 2 or 4 screws, and there are no additional
plumbing connections (if I'm thinking of the right boiler). The tricky
part is that it's behind the gas valve which makes access harder (I
was also replacing the gas valve, so I had the valve out at that point
and just protected the exposed gas pipes from getting water in them).
Also, make sure you release the heating system pressure, or ~5 litres
of water will spray out from the pressure vessel all over the
electrics when you unscrew the plate exchanger -- it should say this
in the servicing manual.

However, I don't want to push you into doing something you are
uncomfortable tackling, and I would suggest you find another
heating engineer.

--
Andrew Gabriel