Just caught up with this thread and noticed the reply from Fred which
implies he's in Sheffield.

I've had three Sheffield plumbers round to quote for a straightforward
replacement of a gravity hot water system by a combi.
The first quoted £3800 all in for a condensing Vaillant.
The second quoted £1230 all in for a non-condensing Ferroli, but he
wasn't Corgi registered.
The third told me that the condensing boiler regulations coming in
next April have been dropped, so I didn't bother him for a quote.
A fourth didn't bother to get back to me after leaving a message on
his answerphone.

Fred, would you be able to tell me who in Sheffield you got quotes
from, who got the job, and whether you were satisfied?

If you prefer not to broadcast advertising, you can reply direct by
turning the invalid into a com.

Rob