MY house already has a conventional boiler (with tank) supplying Hotwater and Central Heating for the whole house (inc bathroom) - it works well. I'm now considering installing 4 ensuites to the 4 large bedrooms. We plan to install a seperate Hotwater system. I need your advice on choosing a Combi boiler which will only supply hot water for these 4 ensuites? What power/type/brand/model should I choose? Many thanks!
you could be heading for a costly mistake - a combi boiler will only be able to service one shower at a time. you will need a hot water storage cylinder to provide sufficient for them all, and even then you may have issues with pressure drop if running more than one shower at a time from gravity fed. and pumps for four showers will drain even a big tank very quickly especially if the gravity replenishment can't keep up.
a mains pressure hot water system such as a mega flow may work provided that you have decent mains pressure coming into the house. best off getting a pro in to survey the job and figure out your exact needs.