My mate's central heating system needs to be flushed to get rid of a
build-up of sludge. British Gas came round and told him that although
his boiler is working fine, it is a bit on the old side and it might
be badly damaged when the system is flushed so it would make sense for
him to buy a new boiler. (If he buys the new boiler they will flush
his system for free, if he doesn't, it will cost £400 PLUS the cost of
a new boiler if it breaks during the operation.)

I guess my question is - is he being conned or is there a real chance
of this happening?

Cheers,

JD