Computherm Q4Z Operating Instructions Manual page 5

which do not have a separate thermostat, do not need heating
at all times but need heating when any of the first two zones heat.
The third and fourth zones, similarly to the first and second
zones, have a joint connection point for a zone valve/pump
(Z3-4), too. If the third and/or fourth thermostat (T3 and/or T4)
switches on, then beside the 230V AC voltage appearing at
Z3 and/or Z4, 230V AC voltage appears on Z3-4 too.
Moreover, the four heating zones also have a joint
connection point for a zone valve/pump (Z1-4). If any of the
four thermostats (T1, T2, T3 and/or T4) switches on, then
beside the 230V AC voltage appearing at Z1, Z2, Z3 and/
or Z4, 230V AC voltage appears on Z1-4 too. This Z1-4
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