Wiring Digital Thermostats and Taco ZVC406

amd

We have 6 zones of hot water radiators. The 6 legacy thermostats (used for heat only, not AC) are wired to a Taco ZVC406 zone valve control unit with 2-conductor wiring. In turn, the ZVC406 is controlling 6 Taco zone valves, each a model 570-2.



We recently upgraded to digital thermostats that integrate with a home automation system from Control4. The wiring diagram (attached) on the ZVC406 instruction sheet does not indicate how to wire a thermostat with more 2 conductors. These thermostats want power as they use the 24VAC for wireless communication in addition to calling for heat. It has a battery, but the battery only lasts a few days if the unit lacks external power.



I have two questions. 1. Is there a recommended approach to wire a digital thermostat like this that needs power from the Taco ZVC406 zone controller (I do not see any "COM" terminal)? 2. Must I run new multi-conductor wiring from tstats to the zone controller to replace my existing 2-conductor wiring, or could I instead install an auxiliary 24VAC transformer somewhere closer to the thermostats themselves, thus simplifying my wire fishing task?



Thanks in advance!

Alan (California Radiant) Forbes

Power Source

The thermostats don't care where they get their power from.  You could tap into the 24 volt terminals marked "Power In" on the upper left side of the ZVC-406 or provide a 24 volt transformer closer to the thermostats.  If you use the ZVC-406, add up the power consumed by both the thermostats and zone valves to make sure the limits of the transformers are not exceeded.