It would depend on how far the 22mm needs to run ie from meter to boiler. Previous poster is right though you do not need 22 all over house. The only reason you need 22mm is because when the boiler plus one other item is in use the pressure will drop and the boiler will not work well. The old boiler probably didnt notice it so bad as it has less gadgets inside to detect a drop, but it would have still lost some of its power.
As far as a refund, it doesnt matter which boiler you choose you will still need the 22mm feed, I think its corgi rules now anyway. It is not the plumbers fault (I am not defending plumbers here by the way, some of them are villians) that you need the new supply. �700.00 does sound ridiculous. So why not get two more quotes to upgrade the pipe to 22mm and then you will know. btw plumbers will work for anything from �150.00 - �300.00 per day