One of the 8 available circuits can be associated with DHW. It is customary to associate the circuit 8 as it is less likely to have been previously used for heating and/or cooling circuits:

If a circuit is associated at the moment the DHW subsystem is activated, the circuit will also result active in Heating and will activates the enabled sources (see https://setecna.atlassian.net/wiki/spaces/PUBDOCS/pages/3258779410).

If no circuit is associated, the current DHW set point is directly passed to the generators in the Opentherm page (https://setecna.atlassian.net/wiki/spaces/PUBDOCS/pages/3258779756):

The choice of not associating a circuit is made, for example, when there is an instantaneous boiler when there is only one Opentherm generator than can manage DHW production by itself.