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Nest Thermostat showing 36 Volts

Oregonian
Community Member

Yesterday I installed a Nest Thermostat on my 20 year old Ruud heating and AC system. I have the following wires connected to the thermostat: R, W, Y, G, and C.

The thermostat appears to be working OK as the heat and AC come on when commanded.

However, I have noticed that the thermostat shows the Voltage to be approximately 36 Volts. My understanding is that the thermostat is only rated to work up to 30 Volts.

Do I need to have my system looked at by a professional to see why it is showing 36 Volts? Or does anyone here have a suggestion on why this is happening and if it needs to be corrected?

Thanks for any suggestions.

1 Recommended Answer

Markjosephp
Community Specialist
Community Specialist

Hi Oregonian,

 

Thanks for letting me know. It appears that you have a Nest Thermostat 2020 model based on the power information you're getting.

The Voltage Open Circuit (VOC) is typically 34 volts, with a normal range of 29 to 42 volts, which are normal readouts from your system to your thermostat. The LIN for this model is different from that of the other Nest Thermostats. With a common wire or a Nest Power Connector, the readouts should be at 385. This is the maximum current draw from all the wires connected. Also, your thermostat detects the wires mechanically but not electrically, which is why you're getting the "Unconfigured" or "undetected wires" message. The wires must be updated using the Google Home app. Please try these steps:

 

  1. Select your thermostat on the home screen and tap Settings.
    1. Thermostat > Wiring > Update.
  2. Ensure that all the wires connected to its base are selected.
  3. If others don't appear, you might need to perform a factory reset on your thermostat to reconfigure which wires you have by adding it back again in the Google Home app.

 

Please let us know how it goes.

 

Regards,

Mark

View Recommended Answer in original post

6 REPLIES 6

Markjosephp
Community Specialist
Community Specialist

Hello Oregonian,

 

Thank you for taking the time to let us know about your inquiry. I'm happy to help.

An Overcurrent may occur with your system's voltage, as the Nest Thermostat's voltage requirement should be between 20 and 30 volts. You need to reach out to an HVAC technician to step down the transformer to make it compatible. Please have a look at this article and let us know if you need more help.

 

Regards,

Mark

Thanks for your reply.

While I was waiting for a response, I found this article which seems to indicate that the Nest should be OK with up to 42 volts. Is this incorrect? Please look under the section labelled "Power". 

I have noticed that the Iin value is 385 which seems excessive. According to the above article, it should be 100-200.

Lastly, today I am getting the following message regarding my wiring: Unconfigured and undetected wires. In addition, the Y, W, G, and C wires are shown in blue. The C wire (which I have connected) is shown in a lighter color (gray?) and it also shows *OB in yellow. can You help me understand what this means?

Thank you.

Today I had an HVAC technician come to our house and look at our installation. He measured all the voltages at the thermostat and in the furnace. Everything looked normal with the voltage being approximately 27 volts. We also saw that the transformer in the furnace is rated for 24 volt output. So, the issue is not the furnace transformer. However, my Nest thermostat still shows the voltage at 36 volts and the current at 385. The technician tried various combinations of wiring but could not get this thermostat to show the correct voltage.

The only assumption I can make is that the thermostat is defective.

Please see my other comment in this thread from yesterday and let me know the answers to those questions -- especially the one about the document I found which indicates that the Nest thermostat should be able to handle up to 42 volts. Is this correct?

Thank you.

Markjosephp
Community Specialist
Community Specialist

Hi Oregonian,

 

Thanks for letting me know. It appears that you have a Nest Thermostat 2020 model based on the power information you're getting.

The Voltage Open Circuit (VOC) is typically 34 volts, with a normal range of 29 to 42 volts, which are normal readouts from your system to your thermostat. The LIN for this model is different from that of the other Nest Thermostats. With a common wire or a Nest Power Connector, the readouts should be at 385. This is the maximum current draw from all the wires connected. Also, your thermostat detects the wires mechanically but not electrically, which is why you're getting the "Unconfigured" or "undetected wires" message. The wires must be updated using the Google Home app. Please try these steps:

 

  1. Select your thermostat on the home screen and tap Settings.
    1. Thermostat > Wiring > Update.
  2. Ensure that all the wires connected to its base are selected.
  3. If others don't appear, you might need to perform a factory reset on your thermostat to reconfigure which wires you have by adding it back again in the Google Home app.

 

Please let us know how it goes.

 

Regards,

Mark

Yes, I have the 2020 Nest Thermostat - not the Nest Learning Thermostat. Thank you for confirming that the voltage and current I am seeing on the display are correct. 

I updated the wiring through the Home App and now the thermostat seems to be working properly.

Thanks for the help.

Markjosephp
Community Specialist
Community Specialist

Hello Oregonian,

 

Sounds great! I'm glad to know that it worked. It looks like we have come to a solution, so I'm going to lock this thread within 24 hours. If you have any other concerns or questions, please feel free to create a new thread.

 

Thanks,

Mark