Christian McArdle wrote:
They are now saying that they can't instal a combi and we can only
have a normal boiler.

Whilst I believe that BG prefer barrier pipework, there shouldn't be any
difference between a combi and a system boiler, so it makes no sense that
they would fit one, but not the other. Very odd indeed, particularly as it
is the primary circuit (which is identical) that benefits from the barrier.
The mains water supply is so full of oxygen already that a lack of oxygen
barrier is of no relevence whatsoever in the actual hot water pipework.

My husband has spoken to some of his friends and they have combi
boilers with plastic pipes and can't see what the problem is.

Indeed.

Christian.

Best guess would be that they underquoted for the work and prefer the
simpler option of just replacing like for like instead of changing the
system and using any old crap excuse to do this.