C wire hook up on the TACO box

[BrokenOldBottle]

I have an existing thermostat running on two wires with batteries and I want to replace it with a nest thermostat that requires a C wire. I do have a third wire available to me I just need to know where to hook it up on the TACO Box

[laurentbourg · Accepted solution]

There is a C connection hub, typically located on the left hand side of your Taco, it might also say 24V. What is the exact model of your Taco control module?

[laurentbourg]

Correct, good luck for tomorrow

[Thekideo]

I hooked it up the way that we talked about and now I'm getting no power on the thermostat display

[laurentbourg]

Did you go to the settings on the thermostat (on the device itself) and enable the power connector? I think there is a special setting for it in the menu of the Nest thermostat 2020. 

[Thekideo]

I only see an option where it says to disable so I assume it's already recognizing it?

[laurentbourg]

should be. and I assume you have the latest version installed? on your thermostat device, settings -> version -> update

[Thekideo]

Yeah latest software is installed.

[Thekideo]

 would pic 2 work ? 

[Thekideo]

 

[Thekideo]

It's crazy doesn't matter what the wiring configuration is it always says no power.

[laurentbourg]

pic1 should be the proper diagram. Zone valve v and all the white wires in junction box is where the R and W from thermostat used to connect before you installed the Nest power connector right? Also you do see voltage between R and W when testing wires with a multimeter at the thermostat, correct?

[Thekideo]

Correct.  From T to R & W in the junction box. R goes to Zone V .. White' are all together.  I hooked up my old thermostat for now just to have heat. If I pull that off and measure it I have 26 volts across r&w. If my understanding is correct, The Nest power connect gets connected inside the junction box.  From Nest WY to W from T.   R to Red.  C to trans.. R to zone, WY All whites.thamks again

[laurentbourg]

Your wiring seems correct. And I assume you did not connect the C on wire plate of the Nest thermostat?

[laurentbourg]

I don’t think it’s worth wasting time on the Nest power connector, as we previously discussed replacing the current thermostat or buying an additional plug-in thermostat is the way to go since you have a free wire for C and a multi zone system. Here is some additional info on wiring your C with your existing thermostat, take a look and make sure that’s what you had previously done. https://www.doityourself.com/forum/boilers-home-heating-steam-hot-water-systems/514502-need-c-wire-b...

[Thekideo]

I was pretty much thinking the same thing last night. If anything I've learned my system very well lol ! I'm at the point I'm not sure if I should just scrap the whole Nest idea and go to a Wi-Fi Honeywell? But I may run into the same issue. Wasn't sure if I should just upgrade to a bigger transformer? Or just add a secondary transformer for that circuit. I really do appreciate all your help. Every time I'm in a jam ,it's like you're on call.. lol

[laurentbourg]

I would keep the Nest, they look nicer in my opinion and once your setup works you should be good to go. Getting another transformer for the thermostat will work for sure, go with that approach if you want to be safe. Replacing the current one should work as well, too bad you got a bad one last time and you couldn’t get it to work. 

[Thekideo]

For sure. I didn't even think about checking the output of the new transformer until hours later.. going in was fine power coming out with zero =totally disgusted. I think I'm going to pick up a new transformer replace the old one and use the C wire and start from there. For some odd reason if that doesn't work then I would use a secondary transformer just for that. Thanks again for everything I will keep you up to date on how I make out 👍

[laurentbourg]

Sounds like a plan, good luck. 

[Thekideo]

Would you happen to remember the link you sent for transformer? Not the plug in style , the Honeywell that gets wired in?

[laurentbourg]

https://www.homedepot.com/p/Honeywell-Home-24-Volt-Transformer-AT72D/202264717

[Thekideo]

Extra wire hook to transformer measured at junction box 27 volts. At the back of the thermostat  R to C 27V.. this is starting to drive me nuts

[Thekideo]

Install the new transformer and was still getting low power on C wire. If I go ahead and install the second transformer I just took out I would put spare thermostat wire to c on transformer. Do I need to hook anything up to R/load  transformer ? This is starting to drive me nuts but I'm determined to figure it out.. or just throw in the towel. ,🤔🤔 Thanks again for all your assistance it really is greatly appreciated

[laurentbourg]

it is strange that it does not work with the new transformer. If you want to use it as a second transformer dedicated to powering your thermostat, you need to plug R and C on it. Do not wire C on the old one. Also double check your wire diagram on the google home app to make sure the C is recognized. 

[Thekideo]

Luck of the Irish I guess..lol do you think the Honeywell ra832a has anything to do with it? I was also thinking maybe because I have three zone valves that's drawing too much from the one transformer? It's weird when I look at the voltage on the nest display it seems to be steady, but the Lin jumps all over

[laurentbourg]

That’s a good assumption that all 3 zone valves running could possibly not leave much current for the thermostat, those valves are probably NC solenoids and therefore constant current current is required to keep them open. Just dedicate that new transformer to powering your thermostat per previous post, that has to work, otherwise you Nest is most likely defective. 

[Thekideo]

Exactly. So from what I remember T wire to junction box. Red goes to Zone valve, W goes All whites tied together. So if I'm correct with (2) transformer I can mount on same box tie into load. I would unhook W from all tired together.& Run to C to (2) trans. The R from (2) trans goes to Zone Valve?

[laurentbourg · Accepted solution]

First transformer is exactly like your original system, which should be red/R to zone valve and W to all white wires. The second transformer load also goes to Red/zone valve, but the common of the second transformer goes to C. Nothing goes to W from the second transformer, and nothing goes to C from the first transformer. 

[Thekideo]

Understood. First transformer everything stays the way it . Second transformer load goes to the first zone valve so it'll be two red wires in there now. And my C wire from 2n trans  goes to the spare wire on the thermostat

[laurentbourg]

Correct

[Thekideo]

👍. So I hooked up the second transformer like you said. Looks like it's working but look how high the readings are should I be concerned?

 

[laurentbourg]

Great to hear it worked out. Those power numbers look good. 

[Thekideo]

Thank you so much for your help I really do appreciate !! When I first saw that voltage I was like man hope that doesn't catch on fire..lol 

Thanks again

Chris

[laurentbourg]

No worries Chris, happy to help. That second transformer will be plenty to power all your other zone thermostats should you choose to upgrade them as well so you should be all set.  

Happy Holidays. 

Laurent

[Thekideo]

Happy holidays to you as well and a happy and healthy New Year

[Thekideo]

If I decide to install the nest on the second Zone. Utilizing the second transformer. Spare wire from T would go to C on  trans. R goes to ZV. Would I just double up those wires on the transformer connection? Or make connection somewhere else

[laurentbourg]

You would just double up like you said. 

[Thekideo]

Understood. I thought the voltage would be too high and I turned my house down..lol thanks again for all your help! Have a merry Christmas, happy holidays and a great New Year if I don't talk to you

[laurentbourg]

Thanks Chris enjoy the holiday period as well

[Thekideo]

Just wanted to double check before I wire all up. Original transformer , stays the same with red wires going to zone valves. And all white's together. New transformer load goes to Zone valve that already has red wire. That would be (3) wires all together zone, red from thermostat & load wire.  The C from trans goes to C wire on thermostat. 

 Wasn't  sure if the RA823A would effect anything or not. Thanks again

Chris

[Thekideo]

Hey quick question. If I leave the original thermostat wired up as it was. All the whites together and red going to zone valve. Then with mew transformer ,you want  spare wire at thermostat  to to C on transformer. Load would go to zone valve. Wouldn't that then put 48 volts at my zone valve? Because I would have two red wires going to that zone valve

[Thekideo]

Wires from sec trans, R goes ZV. C from trans goes to spare wire on T.  For 2ND Nest T to be installed. Do I run two more wires off of trans? I assume R.to ZV &  C from trans to spare wire on T. Wasn't sure if I doubled up wires on thermostat or do something different?