"Richard" wrote in message
...
How do I descale the heat exchanger on my gas fired central heating
system.

Not really an answer - but my father in law was told that the rattling noise
on his 4 or 5 year old, wall mounted, boiler was due to scaling up, and that
he needed a new heat exchanger, and surprise surprise this wasn't covered in
his service plan. He asked the engineer how this scaling had occurred in a
sealed system (not combi), that the same large ex nationalised company had
maintained since installation - cue no good answer. It took us about 30
seconds to fix the rattle - the casing was slightly loose and vibrating
against the wall!

Andy