Hi all,.. just asking this question out of curiosety really....My sister has just had a repair to her boiler,involving renewing the flue fan, replacing the insulation and replacing the rubber o rings on the heat exchanger connections,the engineer also fitted a larger external expantion vessel on the central heating pipe,not sure if its on the flow or return,but the question is,what would be the reason for the external expantion vessel,..she wasnt there when he called so was not told what had been done in any detail......£285,including a service,does that sound about right,..