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How to get Nest thermostat working with hydronic heating + AC system?

How to get Nest thermostat working with hydronic heating + AC system?


  #1  
Old 04-07-23, 02:16 PM
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Question How to get Nest thermostat working with hydronic heating + AC system?

Hoping someone knows the answer to this!

We just moved into our new home and wanted to install a Nest thermostat. There are currently two thermostats in the house, one on the main floor that has 4 wires (Green (G) wire, White (W) wire, Black (Y) wire, and Red (R) wire with bridge to Rc), and one in the basement with 2 wires (White (R) wire and Black (W) wire). We have a Taco SR503 3 Zone Switching Relay, and the main floor thermostat is set as Zone 1 and the basement thermostat is set as Zone 2.

We only have the one Nest currently, and as the basement thermostat is only used to heat the basement, we want to install the Nest on the main floor thermostat, which controls the heat and cooling for the rest of the house.

The heating system is a tankless gas-powered hydronic system connected to a forced air blower, with an air conditioning system connected to the same blower.

We tried to install the Nest on the main floor but it wasn't drawing enough power without a C wire, so we figured we'd have to get the Nest Power Adaptor.The instructions said if you have more than one thermostat to install the power adaptor into the switching panel, which we did.

We connected the white C wire on the adaptor to the COM terminal, the white R wire on the adaptor to the R terminal in Zone 1 on the zone switcher, the white W wire on the adaptor to the W terminal in Zone 1 on the zone switcher, the grey R wire on the adaptor connected to the thermostat R wire with the provided clip, and the grey W wire on the adaptor to the thermostat W wire with the provided clip.

We turned the system back on and the Nest does not seem to be getting any more power, and when we turn on the heat the zone switcher keeps clicking on and off without anything happening.

Does anyone know what we did wrong?

The only other thing we think could have been the cause is that we are actually supposed to install the power adaptor inside the Unico System HVAC and not the zone switcher.

Any help would be greatly appreciated!

Taco SR503 Zone Switcher

Nest Power Adapter connected to Zone 1 terminals and thermostat wires

Heating system

Heating System

Basement thermostat (Zone 2)

Nest power adapter connected to COM

Main floor thermostat (Zone 1)

Unico System HVAC

Taco SR503 Zone Switcher with Nest Power Adapter installed
 
  #2  
Old 04-08-23, 02:51 PM
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When a thermostat has both Y and W the Nest Power Connector needs to attach to the Y. So you need to find where the thermostat cable comes in to the HVAC system.
 
  #3  
Old 04-10-23, 09:59 PM
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Welcome to the forums.

Thanks for handling the thread Astuff.

So as mentioned.... you need to locate where the four wire thermostat cable connects to the Unico air handler. I'm guessing that's one of the high pressure units. I have the M manual open. Post a picture of the wiring or the model number.

Does the Unico also supply heat ? It shouldn't and there shouldn't be a W wire connected.
Your Nest stat must have two R connections.... Rc and Rh.

 
 

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