Help with NEST on TACO 571-2

HeatingHelp

This discussion was created from comments split from: Taco Zone Valve Wiring.

rahm0809

Hi all, need some help. Trying to install a nest thermostat but having issue with power on the R connection. This is the setup the house came with and heat is working fine. I tracked down all the wires to identify and created the diagram. Please let me know what should be my connection. Also added the furnace diagram as well.

EdTheHeaterMan

@rahm0809 This discussion is from 2021, You might think of starting your own discussion. Adding new questions to old discussions can become confusing.

start with +New POST. be sure to select a category topic like Thermostats and Controls
. If you don't select a category then you will get an error and your discussion will not post

Looking foreword to helping you.

Perhaps @Erin Holohan Haskell can help here. maybe the title is Help with NEST on TACO 571-2

Jamie Hall

It would have been better had you started a new thread, @rahm0809 , but since you didn't..

If your diagram really is correct, you will need to swap R and W on all your thermostats. Then you should be able to connect C on the three wire thermostat to the minus terminal on the transformer.

EdTheHeaterMan

If I look at your diagram and compare it to the factory recommended diagram, there are some subtle differences. Those differences will not matter in your current situation. BUT when you need to use the C terminal from the transformer to power up a smart thermostat, you will have a problem.
Look close at the factory diagram. The R from the transformer (in your cane the +) goes to the R on the thermostat. In your diagram the R (or +) from the transformer goes to the W on your thermostat. That makes it impossible to connect the C wire and power up your thermostat's brain. (Brain = WiFi and related internet function of the thermostat)

The W from the thermostat MUST feed the #1 on the zone valve.
In your case the R from the thermostat goes to the #1 on the zone valve.

Now, even though you are wired slightly Bass Ackwards, It still works. But as I said above, it will not work with the smart thermostat.

IMPORTANT. You must wire both the zone valve identically. If you try to correct only the T1 thermostat and zone valve, and leave the other zone valve as it is, then there is a reasonably good chance the you will let ALL the smoke out of your transformer. Then you will have no heat.

Are you confident that you can rewire the Taco 571-2 valves correctly, or is this a little more than you are interested in trying to handle?

rahm0809

Thanks for your comments. I tried swapping R to W only on one thermostat and connected the C wire to that thermostat and the furnace but it was power circling every minute or so. I will try swapping both thermostat and see what happens. 

neilc

read the caution in Ed's message above

EdTheHeaterMan said:

IMPORTANT. You must wire both the zone valve identically. If you try to correct only the T1 thermostat and zone valve, and leave the other zone valve as it is, then there is a reasonably good chance the you will let ALL the smoke out of your transformer. Then you will have no heat.

Jamie Hall

I wonder what's burned out now?

EdTheHeaterMan

rahm0809 said:

Thanks for your comments. I tried swapping R to W only on one thermostat and connected the C wire to that thermostat and the furnace but it was power circling every minute or so. I will try swapping both thermostat and see what happens. 

Taco zone valves have a NORMAL operating condition that NEST thermostats may consider as an error. look at this thread about using an isolation relay. https://forum.heatinghelp.com/discussion/comment/1706292#Comment_1706292
@HomerJSmith posted a great diagram on the use of the isolation relay.

rahm0809

Thank you. If I am reading and understanding correctly, I should be connecting according to this diagram , is this correct?

EdTheHeaterMan

Nope. you need to go to the zone valve transformer


You may also need the isolation relay if this does not work

rahm0809

Hi Ed, thank you for your help… I am bit lost now. Did u mean I have to make another connection from W to the negative of the transformer? 

rahm0809

Just saw the your update on the diagram. I will setup the connection tomorrow in the daylight and let you know. Thank u so much for your help. Happy new year.

EdTheHeaterMan

rahm0809 said:

Just saw the your update on the diagram. I will setup the connection tomorrow in the daylight and let you know. Thank u so much for your help. Happy new year.

I have a suspicion that the NORMAL Taco 571-2 operation will reveal itself as an error. If it does that, you will need the isolation relay. This is how the Zone Valve "Heat Motor" works:
Notice the lines that I have underlined in RED. The NORMAL interruption of current designed into the "heat motor" is interpreted as an error by the Nest AI circuits.

The isolation relay fools the thermostat by isolating the heat motor from the thermostat.

EdTheHeaterMan

Many will recommend the RIB relays because they are very universal and easy to install.
https://www.supplyhouse.com/Functional-Devices-RIBU1C-Enclosed-Pilot-Relay-10-Amp-SPDT-w-10-30-Vac-DC-120-Vac-Coil
I have updated your diagram to the color code of the RIB U1C diagram

Erin Holohan Haskell

EdTheHeaterMan said:

@rahm0809
Perhaps @Erin Holohan Haskell can help here. maybe the title is Help with NEST on TACO 571-2

Got it. @rahm0809, I've moved your discussion to a new thread here.

Thanks @EdTheHeaterMan!

SteveSan

Please see the attached how to wire a Nest to Taco 570 series zone valve.

hot_rod

Nesters don’t seem to want to share the power draw of the stat, they suggest adding their 15Va transformer. It would be nice to have that info to be sure your transformer is adequate

Three of those zone valves 24 X .9= 21.6 Va per zone valve, so 64va for just the valves, if you go by the numbers. Although you often see 3 wired to a 40Va transformer.

The question for Nest, does the battery trickle charge always, or when it gets down to 3.6V the minimum required to keep it alive, does it fast charge and pull a bunch of amps.

Steamhead

Or, you might let Taco do the engineering work for you:

https://voomisupply.com/products/taco-zvc403-4-3-zn-zone-valve-relay-control?currency=USD&variant=40792913444975&gclid=CjwKCAiAwc-dBhA7EiwAxPRylJFS_eg9taDKnwnYQx6zsIGTHqUMLeD7xn4WjqoypkgH_FTlUFl9whoCGwsQAvD_BwE

rahm0809

Ed, just finished the wiring per your guidance and updated diagram. Everything went well , tested both thermostat and heat is working great on both zones. Also no error on the nest thermostat. Will keep monitoring it and will add the relay if I see any error.
Don’t know what else to say but THANKS. This forum is hidden gem.