Connection of ATAG ONE thermostats to ATAG QR SERIES BOILER

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You already posted similar question in

ATAG ONE plus BCU module

I have an Atag QR serie boiler, I have two heating zones in the house (top/bottom) and two ATAG ONE thermostats, or I need two BCU modules for this or is one enough? in the module manual, in position C there is a connection for 1 thermostat, what are the D,E,F connections for? If I connect two thermostats for C, D and E, F to terminal 19, 20, 21, 22 in the boiler, will I control two circuits with one BCU? , or I must have two BCUs (one for each circuit)?

Therefor closing this topic as a duplicate.