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4 zone NEST system issue

Hi Everyone,

I recently purchased a home with 4 zones of hot water baseboard heating connected to 4 different Taco zone valves. I am not too familiar with the wiring for these zone valves as I have been spoiled in the past with the combined forced hot air/AC units. The NEST thermostats worked fine for about a month but now they all enter low power mode for about 8 hours each day to recharge. I am trying to determine the best approach to fixing the problem. Here is what I am working with

Zone 1: 2 wire from Taco/4 wire from AC handler
Zone 2: 2 wire from Taco/4 wire from AC handler
Zone 3: 2 wire from Taco
Zone 4: 2 wire from Taco

Is it possible that 4 thermostats is too much for the same 24V transformer?

Based on Google searches, it appears that I can add a common wire from the air handler for zones 1&2. Will the thermostat use the power from the common while the thermostat is in heating mode? Will it stop drawing power from the 2 wire?

Final question: Will my 2 wire zones draw power while the heating system is not in use during the summer? I am not sure when the Nests draw power to charge.


  • Jamie Hall
    Jamie Hall Member Posts: 23,675
    Nests draw a lot of power. They have to, to power the wifi connectivity. Therefore... You really should have, for that many Nests, and independent 24 VAC transformer -- at least 40 volt-amperes and maybe more -- dedicated to powering them. You will need to add a third wire to the two 2 wire zones -- better, a fourth for all four zones. Exactly which terminals should be fed from which wire, and how to hook up the auxiliary transformer to the whole show is above my pay grade.

    As to drawing power when the heating system is not in use? Indeed they will.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    HVACNUT Member Posts: 5,894
    Look at the Taco ZVZ-4 zone board. It will simplify everything and give you the common for 24v power for the Nests.
  • SteveSan
    SteveSan Member Posts: 239
    Just make sure you pre-charge the Nest t-stats and run a "com" wire and you should be fine. You can always call into Taco Tech Support 401-942-8000 Mon-Fri 8am-5pm EST.