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Nest thermostat issues with combining 3 zone hadronic heat into 1

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n247hp
n247hp Member Posts: 8
Hi All, first time poster.

I have an issue at the thermostat where my room temperature keep jumping up to 10 degrees up and then down out of nowhere. This is caused at the line where I combined 3 baseboard heat zones into 1 as I want just the 1 thermostat running it. I have tried different nest thermostats and even switching from dinning room wire to a kitchen wire to see if there was some issue with the line. I am starting to think its the way I combined the 3 taco valves into a single wiring. I essentially combined the red, white and common wires from the 3 valves and then wired them to a single zone between zones 4 and 6 (making sure I keep them on a single transformer). Do you think this could be causing the issues where the thermostats room temp keep moving all over? I have it set to 70 but because it keep jumping it never heats those zones evenly as it keep turning the boiler on and off

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  • HVACNUT
    HVACNUT Member Posts: 5,886
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    I won't ask why, but you could simply remove the wires from R and W in the zone panel for the thermostats you're not using, then jump W from the thermostat you are using to W on the other zones you want to combine. 
    SteveSan
  • SteveSan
    SteveSan Member Posts: 236
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    Like hvacnut has said. If you are looking to control 3 zones with 1 t-stat you just wire the r-w to the first zone and then just jump w-w to the 2nd and 3rd. This can only be done on the zones with the same transformer. So, you wouldn’t be able to control zones 3-4-5 for example. Just 1-2-3 or 4-5-6. Hope this helps.
  • HomerJSmith
    HomerJSmith Member Posts: 2,509
    edited October 2023
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    It takes a lot of juice to run a thermal zv, Make sure you have adequate current to run all three together. In fact, I would use a separate transformer (40VA) to do the job. Terminal 1 & 2 would go to the transformer and thermostat and terminal 2 & 3 would go to the boiler aquastat to turn on the boiler. Since you are running all 3 ZVs at the same time off of one thermostat you would only need a terminal 2 & 3 connection to the boiler off of one ZV, but I would wire up all 3 ZVs in parallel to the boiler or ZV controller. If you are wiring up a Nest themostat follow the diagram below and delete one thermostat and one relay and wire 1 & 2 terminals of all 3 ZVs in parallel. You need the relay and a 3 conductor cable to the Nest.
    As I vaguely recollect someone mentioned that the heater in the ZV would disconnect to keep the valve from over heating. Maybe some one could comment on that as relating to your problem.



  • n247hp
    n247hp Member Posts: 8
    edited October 2023
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    SteveSan said:

    Like hvacnut has said. If you are looking to control 3 zones with 1 t-stat you just wire the r-w to the first zone and then just jump w-w to the 2nd and 3rd. This can only be done on the zones with the same transformer. So, you wouldn’t be able to control zones 3-4-5 for example. Just 1-2-3 or 4-5-6. Hope this helps.

    Thank you for all the responses! So currently I have zones 1,2,3 serving Basement, 2nd floor bedrooms and the living room. The remaining 3 zones (which all had a separate t-stat) are for Kitchen, Dining and a "sun room" which is really part of the kitchen. Those 3 rooms are all really 1 space with very little wall separation. Just to clarify the process of jumping w-w, should I wire the 3 zone valves to say zones 4-5-6 so they all sit on a single transformer and then on the side where the wires go to the t-stat I would have my Red, White and common wires go to the 1 t-stat (say in zone 4), but also I would add the white wires to the zones 5 and 6 on the side where the wires go to the t-stat and wire them to the white wire from zone 4? hope what I am saying makes sense. thank you again!
  • n247hp
    n247hp Member Posts: 8
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    My current setup, works and it activates the 3 desired zones of the single t-stat but the issue is that only on that thermostat where I have 3 zones wired together, room temperature spikes when the zone turns on to heat. So my thinking was that maybe its something with the wiring overheating the t-stat (not sure if that is even possible).
  • hot_rod
    hot_rod Member Posts: 22,467
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    Those are fairly high current draw zone valves, over 1 amp in some cases
    24v x 6 amp= 144 vA
    Looks like you have 80vA available in the relay control?
    Thinks got pretty hot in the upper part of the relay box? Or just the camera flash?

    Transformers have the proper size fuses?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • n247hp
    n247hp Member Posts: 8
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    Just wanted to mention that I switched the zone to a Nest 3rd Gen thermostat from the Learning one and the issue went away. I think that more basic unit was just not able to function properly with how I wired things.
  • paramounthvac
    paramounthvac Member Posts: 1
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    Following. Had a similar issue recently
    - Spencer
    Paramount Heating & Air Conditioning
    Reno, NV
    https://www.paramountnv.com