Hi Ponder,
You are right to feel disappointed on the bad service of the very people experienced, enough to forsee these problems, when you go to view, a house your hoping to buy, you dont always open and shut windows or doors, to check there working, so why would you check the boiler, most of them are covered with an insulating jacket, so if there would be no way of telling if something was wrong with it . Surely this is the job of the seller, estate agent, and major jobs, surveyors, to tell the truth and not try and pull a fast one, then send an engineer in, obviously tell him not to replace the old boiler because of the cost, this takes the biscuit. These people have probably done this sort of thing to many house purchasers.