In this case, the OP would be better sorting out the pipework, getting the
combi supply dedicated back to the stop cock and piped up as I suggested,
get the appliances on cold fill, get rid of the bath, have a flow restrictor
on the sink tap (available from BES), and put in another combi for the new
ensuite. This is "probably" the most cost effective route for him. I await
his DHW demands.

I was wondering when a second combi would come into the discussion