Open vent central heating

Question

is it possible to upgrade a open vent central heating system by
installing a sealed system type high efficienty boiler in order to eliminate the need for a expansion tank in the loft due to the numerous
times the system has over heated and vented steam and hot water.
surely its just a case of installing a new boiler ,using most of the existing pipe work ,rerouting new pipe work,and possibly the need for a
power flush.