Wiring Google Nest Power Connector to Multizone Heating

jrhgto

Hi,

I am a newbie in regard to wiring zone valves, and I currently have an older 2 wire forced hot water heating system using a Burnham boiler connected to 5 heating zones using Taco Valves. I have 2 wires going up to each thermostat and need a way to power my google next thermostat using the Google Nest power connector.

The Zone 2-5 taco valves are daisy chained (terminals 2 and 3) down from the Zone1 valve. Here is a diagram of the setup:



Since I have 2 transformers connected together, does that mean that I have power in both the Red and White wires coming from transformer #1? So the white thermostat wires will have power? (since they are pigtailed to the white transformer wire)

It appears that in my setup, the thermostats will take in power from the white wire and send it to the red wire (T1 on Taco) when it calls for heat? I thought it was supposed to be the other way around?

The Zone1 valve has 3 wires connected to T2 (Boiler white, Transformer Red, and daisy chain to Zone2)

So not sure what to do with all these wires when connecting to the google power connector.

Thanks!

SteveSan

@jrhgto You can purchase a 5 zone Taco zone valve controller ZVC405-4. It will clean up the mechanical room ( wiring ) and also help troubleshoot with it's LED lights on the control. It lets you know which zones are calling and which zones that are not in use. It comes with two 40va transformers, so enough to handle the load from the five Nest t-stat.

The link below is to the IOM for the ZVC405-4.

If you have any questions, please give Taco Technical Services a call during normal business hours Mon-Fri 8am-5pm EST 401-942-8000

https://www.tacocomfort.com/documents/FileLibrary/102-395.pdf

109A_5

Hello @jrhgto,

@SteveSan's solution is probably the best solution. In your drawing the two transformers have to be phased to connect them in parallel, so they don't burn each other up.

Anyway;

SteveSan

The control has two 40va transformers connected to the board so no need for external transformers. Wiring is simple, top right of the control board is your R-W-C for t-stats. Bottom right is for your zone valves using terminals 1-2-3 from the 571-2 and left pump end switch is for your pump ( if you need the control to turn it on ). Upper left XX goes to the TT terminals on boiler. Please call us if you have any questions.

jrhgto

Thanks for the replies..Not sure if I want to spend $180 and re-wire something that has been working fine for 27 years.

Would love any other comments on how to wire up the google power connector with my existing wiring.

HomerJSmith

Since you apparently have Taco 3 wire zone valves (570 type?), you can use this diagram. Using a Nest basically uses a third wire for charging the Nest (C wire).

https://www.supplyhouse.com/Packard-PR360-SPST-NO-24V-18-Resistive-Amps-Switching-Fan-Relay

HomerJSmith

The Nest power adapter is basically used for furnace applications, that's my take. I have always pulled a 3 conductor cable to the Nest. I understand that isn't always easy to do. Nest technical should be able to help you. I think that you are going to need a isolation relay for each Nest with a 3 wire Taco zone valve. Or go the SteveSan's route.

Zman

The OP is trying to figure out how to wire one of the common wire workaround devices with his 2 wire system.

Given that you have the most misunderstood zone valve created, you are using a device that was invented by a non-heating company to work in a world they don't really understand, and you probably don't know for sure of the polarity of the transformer, I would strongly recommend installing a Taco controller.

That being said, If the transformer is wired so that the red wires are positive. You should be able to intercept the red wire going from the pigtail at the transformer. The transformer Red connects to the right side and the t-stat R to the left. The white wire from the t-stat to the zone valve would connect to the left side W and the wire continuing to the zone valve attaches to the right side W. The C on the right side gets connected to the white wire at the transformer.

If for some reason your system is not wired as I am assuming, you may end up letting the smoke out of the transformers and you will have a great reason to upgrade to a Taco controller.

HomerJSmith

I might add that two transformer secondaries (24 volt) wired in parallel have to be connected in phase. There is an easy way to do this and a more complicated way. I have always done it the easy way.
There have been another solution, posited, and that is to use a bleeder resistor between the C connector on the Nest and the W1 connector on the Nest. The value was 990 ohms 1/4 watt which is awfully close to 1K ohm. The idea was a small amount of current would flow to the W1 connector from the C connector charging the battery in the Nest.
Disclaimer:
I have never tried this. If I did try this, I would use the wiring diagram that I posted a pic of with the relays, which would separate the two transformers.

EdTheHeaterMan

If you decide to wire it without @SteveSan's control suggestion. I might offer you this non patented device I invented called the SmokeKeeper.

It keeps the factory installed smoke inside the transformer. Saves money on replacement transformers
And if you act now you can get two Smoke Keepers for only $29.95 plus shipping and handling of $25.00 in the 48 United States and some parts of Alaska.