Nest Power Connector

[DrRon]

Hi, I have four heating zones and all thermostats are older Honeywell systems with two wires - red and white. I want to change one of these to a NEST thermostat but received the message that a power connector was needed.  Unfortunately the instructions and YouTube diagrams do not match my system. What I have are four Taco zone valves on the boiler. Coming from the thermostats each red wire goes directly to its respective Taco valve first terminal  while each white wire goes into a bundle capped together.  The second terminals are connected to each other with a white wire from one to the other. The third terminals are connected to each other the same way with a red wire. 

The first Taco in the series (not the one where I want the NEST connected) is connected to the transformer with a white wire to the second terminal and a red wire on the third terminal. There is another white wire on this valve that runs from the second terminal to the white wire bundle from the thermostats, making five wires in that bundle. 

I would like to connect the power connector to the last Taco valve connector in the series. Any suggestions or solutions? 

Thanks for any assistance - Ron

[Patrick_Caezza]

@DrRon 

Taco Valve controllers are a pain to connect to any smart thermostat.

Can you post a picture of the Taco controller showing how they are wired and which model they are,

[DrRon]

I don’t know how to tag you, sorry. Hopefully you see this. The red and white wires with the curling go from one Taco to another. The red wires not curled (terminal 1?) go to thermostats. The Taco on the right is directly connected to the transformer. I would like the Nest connected to the Taco on the far left. The red twist wing in the middle of the picture is where the four white wires from the thermostats are bundled. Also in that bundle is a fifth white wire that goes to the terminal on the right Taco where the white wire from the transformer is connected. They are Taco 571 valves. 
Thank you!

[Patrick_Caezza]

@DrRon 

 For each valve to which you want to add a Nest Thermostat, follow this wiring. Depending on the size of the 24VAC transformer, it may or may not work. As I mentioned earlier, connecting to one of these is a hassle.

If this doesn't work, you could try using the Nest Power Connector with an external 24VAC transformer.

Ultimately, a relay may need to be inserted between the Nest and the Relay. But that is a last-ditch effort

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