See Within one dwelling we will aggregate the DHW and CH flows/powers using the “maximum method“ as explained in https://hysopt.atlassian.net/wiki/spaces/HRM/pages/3089367263/Step+6+aggregation+of+the+DHW+flow+power+with+the+CH+flow+power#Maximum-of-central-heating-and-diversified-DHW-flow .
Why? Either the HIU is in DHW tapping mode, either the HIU is in CH mode.