Nest t-stat with taco zone board

Snowmelt

I called my local rep up , told him that the new customer had 3 zone’s, 2 of them where nest thermostat.

The rep told me that taco includes some transistor, I believe he told me that jumping c & w with I think 10 k, he also told me to use the centry zone valves which I been using lately. I am going to install the 0015 circulater and try the WIFI out

Dave H_2

@Snowmelt

It depends upon which Taco zone board you have.
The ZVC controller may have enough horsepower with the transformer built in
The SR panel does not, you may need an external transformer to run those stats

Dave H

EBEBRATT-Ed

@Snowmelt

I beleive you mean "resistor"

I guess some electronic thermostats that steal power will not work well with some controllers and relays so the fix is to put a resistor in.

I just found out about his recently myself (the hard way)

Snowmelt

Yea Dave it’s actually a ZVC 3 zone but only 2 nest,

HomerJSmith

So, what's your complaint?

Nest thermostats need 3 wires going to it. An R wire that's always hot, a W wire that turns on a device, usually a relay, and a C wire that charges the Nest. The R & C wire charges the Nest.

If you don't have 3 wires going to the Nest, it isn't going to operate properly.

Where did the Tech say to put the 10K resistor? To charge the Nest it would be in the Nest, if there are only 2 wires going to the Nest, I would think.

Jamie Hall

You really can't just throw in a resistor and hope for the best. It depends on the control and the wiring. The basic problem, though is pretty simple: the Nest (and most other wi-fi themostats) actually requires a fair amount of power to keep charged. If they have three wires, R and C do the job, no problem (sort of -- see below). If they only have two, though, they are going to try and draw that power through whatever those two wires are attached to. You wind up with two basic scenarios: in the one case, the thermostat will draw enough current through the attached device to turn it on -- or try to. Won't hurt the Nest, but may cause erratic operation of the attached device (or even burn it out). In the other basic case, they can't draw enough power, run out of charge, and then the thermostat itself will be erratic or fail to operate. There is a subsidiary case: there simply may not be enough power available from the attached device to power the thermostat -- and this can happen with three wires as well as two.

If you are going to put in a Nest or other wi-fi thermostat, use three wires or an auxiliary power source.

Snowmelt

Complaint is there is only two wires and the nest system is working

stonebutson

Resistor goes in series with R? Limits the current to keep the relay from chattering? I can’t get any information on these things. People get them at the home center and install them then I (we) get to deal with it.

HVACNUT

> @stonebutson said:
> Resistor goes in series with R? Limits the current to keep the relay from chattering? I can’t get any information on these things. People get them at the home center and install them then I (we) get to deal with it.

The resistor goes between Common and W, or the load side of the thermostat.
The idea being, when the thermostat is not calling (open), the Common from the system transformer will bleed through W to power the thermostat rather than through the relay coil. Which is kind of like going the wrong way down a one way street.

SteveSan

Nest suggests to use a 220ohm 5watt resistor with their t-stats. Our 1000ohm .5watt doesn't work with Nest t-stats. Also the Nest needs to be pre-charged before wiring to our ZVC's or SR controls. Any questions please call into Taco Tech Support 401-942-8000 we are here Mon-Fri 8am-5pm EST.

STEVEusaPA

Rather than always wonder which resistor to use, and have on hand, and have for replacement, wouldn't it just be easier to swap out the control panel with the newer ones?
Seems easier than having a kit of resistors on my truck, with a chart I'll need to update of every type of t-stat that may cause this issue.

pecmsg

STEVEusaPA said:

Rather than always wonder which resistor to use, and have on hand, and have for replacement, wouldn't it just be easier to swap out the control panel with the newer ones?
Seems easier than having a kit of resistors on my truck, with a chart I'll need to update of every type of t-stat that may cause this issue.

Easier to Loose the NEST...………. Problem Fixed!

Dave H_2

here is the wiring with ZVC controllers. Please note what @SteveSan said about what size resistor to use. My drawing shows the resistor that comes with the Taco panel.

Dave H

Ron Jr._3

The Nest thermostat does work with only 2 wires connected to RC and W for heat. They'll have to pull the thermostat off the wall and periodically charge the hockey puck up with a micro-USB power source.

We replaced a boiler a few years ago and had a zone connected to a Nest with just 2 wire. Customer installed it 2 years prior without charging. Wifi connected too