Nest thermostat detects C wire but says no voltage

[Tpbuckley]

Hello- I have two nest learning thermostats, both third generation. The unit on my first floor is connected just to the heating system, the unit on my second floor is connected to both heating and air conditioning( 3 zone heating system and 1 zone central air).

The unit on my second floor (ac and heat) keeps draining the battery. I have removed the unit and charged it, after reading more about this issue I found out it needed a c wire.  I went to my furnace and ran the common from the transformer through the blue wire and landed it on the C terminal on both thermostats. The thermostat on my 1st floor (just heat) sees the wire and the power no issue.  The unit on the second floor(heat and ac) sees the wire is landed but says there is no voltage. I checked with a multi meter and the voltage is present between the RH and C terminal. I also swapped the 1st floor and the second floor unit. Both units when connected to the first floor base see the wiring and report no issue and charge. Both units when connected to the base on the second floor state there is a wiring issue and no voltage on the C wire. 

Is it just a bad base? Any other steps I should try?  Thank you all for your feed back.  

[RenzJ · Accepted solution]

Hi  Tpbuckley,

Thanks for reaching out to the Google Nest community.

I appreciate the steps you took to isolate the issue. Let’s check a couple of things that might affect this. What type of Nest Thermostat do you have?

Let’s gather power readings for the second-floor Nest Thermostat. Follow the steps below:

For the Nest Learning Thermostat and Nest Thermostat E:

1. Press the thermostat ring to bring up the Quick View menu.
2. Turn the ring to Settings and press to select.
3. Turn the ring to Technical Info and press to select.

For the Nest Thermostat 2020:

1. Tap the touch bar to bring up the menu view.
2. Slide your finger down to Settings, then tap to select.
3. Slide your finger to Equipment > Power Info.

I look forward to your response.

Best,

Renz

[RenzJ · Accepted solution]

Hi  Tpbuckley,

Thanks for reaching out to the Google Nest community.

I appreciate the steps you took to isolate the issue. Let’s check a couple of things that might affect this. What type of Nest Thermostat do you have?

Let’s gather power readings for the second-floor Nest Thermostat. Follow the steps below:

For the Nest Learning Thermostat and Nest Thermostat E:

1. Press the thermostat ring to bring up the Quick View menu.
2. Turn the ring to Settings and press to select.
3. Turn the ring to Technical Info and press to select.

For the Nest Thermostat 2020:

1. Tap the touch bar to bring up the menu view.
2. Slide your finger down to Settings, then tap to select.
3. Slide your finger to Equipment > Power Info.

I look forward to your response.

Best,

Renz

[Tpbuckley]

Battery 3.799v voc 4.67 V Vin 4.66 V lin 8mA(o)

[Tpbuckley]

It's a nest learning thermostat 3rd generation 

[Jenelyn_O]

Hi folks,

@Tpbuckley, thanks for the information above. A few questions: you mentioned that you already tried to check the voltage of the wire using a multimeter. Could you please confirm what specific power reading you got from the multimeter? Also, in what country are you located? 

Please reconnect your C wire to the Nest Thermostat. Try to strip and straighten the wire before putting it back to the terminal. 

I appreciate the input, Renz.

Regards,

Jenelyn

[Tpbuckley]

I will take new readings and post them here soon. I just purchased a new volt meter today and I am waiting for it's delivery. 

[Jenelyn_O]

Hey Tpbuckley,

That's good to hear. Through that, we can assure how much voltage is running through the wires. Please keep me posted.

Best regards,

Jenelyn

[Tpbuckley]

Ok I checked the voltages. For the heating equipment between the red wire (RH) and the blue wire (C) I registered 27.8 volts. White(w) to blue(C) 0 volts and red (RH) to white (W) 27.8 volts.  For the air conditioning wiring I have the following  red wire to green was 29 volts, red to white was 29 volts and white to green was zero.  

[zoeuvre]

Hi all,

@Tpbuckley, thanks for the information and I'm sorry for the delayed response. Could you fill out this form so we can dig deeper into this? Let me know once you're done. 

I appreciate your help, Renz and Jenelyn. 

Kind regards,

Zoe 

[zoeuvre]

Hello Tpbuckley, 

Checking back in—we haven't received your form. Were you able to fill it out? Still need our help? 
 

Thanks,

Zoe 

[Tpbuckley]

I missed where you posted that you want me to fill out a form.  Sorry about that reviewing it now. 

[Tpbuckley]

I completed the form.  Let me know if you require any further information. 

[Jenelyn_O]

Hi there,

@Tpbuckley, I received your form. I'll hand it over to our team. Please keep an eye on your inbox or messages as they will get in touch with you soon.

I appreciate the help, Zoe.

Cheers,

Jenelyn

[Tpbuckley]

Great thank you!

[zoeuvre · Accepted solution]

Hello there Tpbuckley, 

Nice! If you run into any more questions in the future, please feel free to create a new thread.
 

All the best,

Zoe 

[Tpbuckley]

Will the people reviewing my form respond here or via email?

[zoeuvre]

Hi there Tpbuckley, 

Please keep an eye on your email, as someone from our team will reach out to you to assist you more.

Cheers,

Zoe 

[Tpbuckley]

Ok I checked the voltages. For the heating equipment between the red wire (RH) and the blue wire (C) I registered 27.8 volts. White(w) to blue(C) 0 volts and red (RH) to white (W) 27.8 volts.  For the air conditioning wiring I have the following  red wire to green was 29 volts, red to white was 29 volts and white to green was zero.  

[LarryTG]

was this problem ever solved?  I have the same issue.  I do not see where it was resolved.  thanks

[Tpbuckley]

No it was not solved, i submitted all of the paperwork back to nest that they requested and nobody has followed back up with me.  Its heating season where i live now so the thermostat is getting its power and charging the battery now when it switches the heat on.  It will die again during the summer without a resolution on their end.

[LarryTG]

Thanks for your reply.  This is a very frustrating situation.  I have no C wire so I hired an electrocution to install a Transformer per the specs and drawings provided by Google Tech.  It is attached to the specified power connector.   It was installed exactly as directed.  I am still getting a message that I must install a  power connector.   The thermostat burns through batteries like crazy.  I am about ready to pull the plug.   What say you?

[Tpbuckley]

So I have multiple nest systems which is why I have stayed with them. (doorbell, door lock, thermostats, smoke detectors) in general I am satisfied with their products. This issue does really bother me though. I have three heating zones, one of those zones also has the central air conditioning connected to it. When I just had heat (before installing the central air) the units had no reported wiring problem even though there was no c wire.  They worked without issue. Once the AC was installed the second unit claimed it had a wiring error. The unit installed where there is no ac had no error. The unit where the AC was installed was ultimately replaced as a warranty replacement after the units battery started draining during the summer months without the heat running(mind you the furnace was still on and sending out voltage to the thermo stat).  Second unit after a year or so started demonstrating the same problem.  This summer the same problem occurred and I said ok I've had enough. I skinned back the cable between the thermostats and the furnace and and landed them on the c wire terminal, then at the boiler I ran a new wire from the transformer and spliced it together with the new c wires I landed at the two thermostats. Boom thermostat with only the heat claims all is good is wired properly, battery charges no issues (it's 5 years old now j think) second unit with the AC  same bs still claims there is a wiring issues etc and if I leave the c wire landed it won't do anything at all.   Now that we are back in heating season it has no issues because it's switching the heat on and stealing voltage when it does to charge the battery. If they don't answer me soon I may *gulp* but another thermostat and see if that solves the problem but this is already the second one.