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Nest Learning Thermostat No C-Wire/No Problems

CubanlinkEnJ
Community Member

Hi everyone. Last month I upgraded my old Honeywell mercury two-wire thermostats, that were used for heat only, to Nest Learning Thermostats and haven’t seen any issues not having a C-wire connected. The thermostats aren't having any power issues, the display turns on when I walk near it, no wifi disconnects, and no error codes. Looking at the tech details, the battery voltage is usually around 3.83V, the Voc and Vin voltages are all nominal, and the Iin reading is getting a constant 20mA charge whether the system is running or not. 

I keep reading things with people saying that the thermostat is pulsing the system to get power and without a C-wire, eventually the thermostats will start having problems or they could mess up my heating system. I’ve had two of them installed for over a month now and haven’t seen any problems or heard any strange noises coming from my heating system at all. They were installed for three weeks before it got cold and I started using heat, and now they’ve been actively calling for heat when required for the past two weeks…again, I seem to have no issues at all. 

I guess my question is, has anybody had a positive initial experience like me, only to start having issues with the thermostats sometime later? I only have two wires going to my thermostat, so in order to add the common wire, I would install Nest power connectors in my zone controller. I’m debating now if I should be proactive and add the power connectors or leave it alone since it seems to be working just fine?

 

Thanks for any feedback.

1 Recommended Answer

Just as an update, I installed the power connectors yesterday and all is working well. I spoke with Taco prior to the install and customer support told me that the board can handle two Nest thermostats at most, but a third thermostat in the future would need to be powered externally.

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15 REPLIES 15

IsaC
Community Member

Hi, I am, I believe, in the same situation - I have power nest connectors that I could install but I can't need any electrician wanting to help me to do that, so I decided to leave this alone for now ... not sure it is the best strategy though. But the thermostats are working so far.

diyx123
Community Member

I had a similar experience.  It's been 1-2 years without "power issues" but I believe I might be having issues now.  Not necessarily Nest related at first.  I am now having issues with the control panel (taco) board.  This could be related to the power stealing nest thermostats, we have 3 of them.  I spoke with Taco support and they insisted that the Nest thermostats give unnecessary stress to the Taco board since it uses it to charge the thermostats. 

I would like to add a fourth Nest thermostat in the basement but I might rewire a common-wire for that zone.  I ordered a new Taco board since mine is over a decade old.  I believe it's cracked or has some solder damage since flexing it causes a signal to the furnace.  I'll be installing the Power Connectors with the new board as a preemptive measure.  This should come standard/optional with all of the Nest thermostats.  Individuals are receiving emails to get the power connector for free.  I think I received an email like that a year ago.  I didn't order them since I wasn't having issues then.  I regret that and reached out to Nest.  They won't issue the connectors without the original email.  Either way I’m adding the power connectors to hopefully prevent any future issues relating to the thermostats.

Sounds like your setup is similar to mine. I have a four zone Taco controller, three thermostats and hot water. I currently have two Nest Learning thermostats for the main floor and upstairs; the third thermostat in the basement is a Honeywell that will eventually be upgraded to another Nest. 

What kind of issues are you currently experiencing? Do you have a common wire or the Nest power connector installed on any of them?

 

I posted this same thing on Reddit and there were a few people that said they had no issues for the first couple years, but as the battery degraded, the charging current wasn’t enough from the system and they started seeing auto focus not working, wifi dropouts, and eventually turning off all together and waking up to a cold house. After installing either a common wire or the power connector, the thermostats began working normally again. 

I ordered the power connectors today as a precaution and will install them in the Taco zone controller this weekend. 

Just as an update, I installed the power connectors yesterday and all is working well. I spoke with Taco prior to the install and customer support told me that the board can handle two Nest thermostats at most, but a third thermostat in the future would need to be powered externally.

EdwardT
Community Specialist
Community Specialist

Hi folks,

 

Thanks for posting. Nest thermostats are designed to use very little power, and in many cases they can use your system’s heating and cooling wires to get enough consistent power. But sometimes, you may need to connect a common wire (C wire) or power accessory, like the Nest Power Connector, to make your system compatible.

 

Thanks,

Edward

EdwardT
Community Specialist
Community Specialist

Hi folks,

 

It's me again. I wanted to check back in to see if you have other questions and concerns. Feel free to let me know if you do. 

 

Thanks,

Edward

What model Taco board are you running?  I spoke to Taco support as well and told them I had 3 and potentially installing a 4th Nest thermostat.  They didn't mention a limit but did recommend the Nest power connectors.  I believe it's based on the AMP rating on the transformer on the taco board itself?

I believe it is related to the capacity of the transformer. I have the Taco SR504 and I’m using all 4 zones; three for heat and the fourth zone set to priority for hot water. 

I currently have Leaning thermostats on zones two and three; zone one is my basement and has a non-smart digital honeywell thermostat. Eventually, I will upgrade it to another Learning thermostat, and when I asked Taco tech support if I could wire up another, they told me the board can only handle a max of two. They sent me a diagram to wire a 24V external transformer in parallel with the third thermostat, but I’m just gonna buy a plug in transformer, snake the wires through the wall, and hook it right up to the new thermostat. You can find the diagram they sent me here http://www.taco-hvac.com/tmp/ExternalXfrmerSR-4Powerrobbingthermostat.pdf

The thermostats are working just as they did before adding the power connectors, but now my battery voltages are consistently about 3.93V, Voc and Vin are equal at about 38V, and the Iin is now a constant 200mA.

Thanks for the info and diagram.  Seems like we have a very similar setup.  I just have one more zone and running a Taco SR506.  Are you using the plugin transformer on just one of the thermostats or all?  I probably could run a C-Wire to the basement and to one on the first floor.  They are relatively easy to access.  The other ones will require more snaking.

My three Nest thermostats are all running 3.8X Volts.

I found a similar thread with individuals whom are experiencing similar issues: "Nest calls for heat and taco registers the signal with a light but won't fire the furnace on"... Problem seems to occur randomly after having the Nest thermostats installed...

https://www.googlenestcommunity.com/t5/Nest-Thermostats/Nest-show-error-code-quot-no-power-to-Rh-but...

I wonder if Taco can beef up their relay system to allow more smart thermostats to be connected.

No direct power issues with the Nest thermostats yet.  I've been only running them for about a year.  I'm currently having issues with the Taco board not firing signals to the Furnace.  Runs fine with just water boiler only.. No Nest is connected to that.. Once the Nest thermostat calls for heat it sometimes doesn't fire the boiler.. Not sure if it's related to the Nest thermostats but it could be.  Replacing the board now and installing the power connectors as well.

Sorry to hear about your issue. When the thermostat calls for heat, can you see the LED activate on the Taco for the zone that’s calling for heat? 

Please let us know how replacing the board and adding the power connectors works for you. 

Thanks.

Yes, the red light registers on the Taco board display.  When the call doesn't fire the furnace, I can flex the board at times and it will fire the furnace.  This is why I'm replacing the board.  Maybe a solder joint somewhere cracked.  Could also be the relays.. fuses look fine.. It's an old board (2007), hoping this fixes the issue along with the Nest power connectors.

It's hard to test because the issue happens at random.  It seems to happen randomly when there's calls for hot water along with heat (Nest thermostat).  Sometimes the furnace will fire, sometimes it won't.  A quick flex of the board, or push in a relay, or turn off/on the power to the boiler, etc. will fire the furnace back up.

EdwardT
Community Specialist
Community Specialist

Hi folks,

 

With the issue that you're having with the HVAC, I would suggest checking our Nest Pro services so they could take a look at your system.

 

Thanks,

Edward

EdwardT
Community Specialist
Community Specialist

Hi folks

 

I wanted to follow up and see if you are still in need of any help. Please let me know if you are still having any trouble from here, as I would be happy to take a closer look and assist you further.

 

Thanks,

Edward

EdwardT
Community Specialist
Community Specialist

Hi folks,

 

I'm just checking in to make sure that you've seen our response. Please let us know if you have any other questions or concerns as I will be locking this in 24 hours.

 

Thanks,

Edward