Ed Sirett wrote in message ...
I can picture it now. The old boiler had a big balanced flue hole and the
installer reused the hole for the flue/duct.

Usually when I come across this situation the old hole is just where you
want to put the fixing for the new boiler...

But, as most new boilers have a top flue, the base of the boiler ends up
lower down than before which, in this case, renders the kitchen worktop
unuseable. I can't believe anyone with an ounce of respect for their
customer would do that, but my experience of plumbers suggests that they
inhabit their own little twilight world where ripping off the customer is
sport.
There are people that, if you give them a tenner, will give it back to you,
and then come and steal it.