On Mon, 08 May 2006 23:59:45 +0100, John wrote:

I am not a plumber or heating engineer.

My sister has a fairly new Combi Boiler, approx 3 years old. It is an Ideal
Mini C24 model. Anyway, it appears that the heat exchanger has 'gone'. She
has had a 'friend of a friend' look at it and he has diagnosed the fault.
He is CORGI registered etc. and is self employed on this basis. He is going
to let her know a price in the next day or so for a repair., but has warned
her it won't be cheap. He said the unit has to be taken off the wall to do
the repair so I am presuming it is the heat exchanger although my sister
thought he said "expander" (maybe something got lost in her understanding).

If it has to be taken off the wall and from what you said this sounds like
the expansion vessel. If it is that and not the heat exchanger then the
cheap way to fix this is not to touch the boiler but fit a separate
external expansion vessel. I think this is in Ed's sealed system faq.