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Nest thermostat with C connector, heat only system, not getting enough power

Mudfoots
Community Member

Hello!  I have a heat only system.  It was two wires, so I installed the C Connector module to run the Nest thermostat.  About every 30-45 days I get a "battery low" message and "need to connect power" message.  I checked the wiring of the C connector and it is to spec, I can only assume the C terminal on my heating unit is not pushing much power.  I do not have a multimeter to check, are there alternatives for connecting the C wire?

5 REPLIES 5

zoeuvre
Community Specialist
Community Specialist

Hi Mudfoots, 

 

Uh-oh! If you have a heat-only system and you're experiencing frequent "battery low" messages on your Nest Thermostat, it could indicate that the C wire connection is not providing enough power to keep the thermostat charged. Here are a few alternatives you can consider to connect the C wire:

 

  1. One option is to use an external power supply, such as Nest Power Connector, to provide constant power to the thermostat. This involves connecting the C wire from the thermostat to the C terminal on the heating unit and then connecting the other end of the C wire to the external power supply. You would also connect the R wire from the thermostat to the Rh or Rc terminal on the heating unit. This setup ensures that the thermostat receives continuous power and doesn't rely solely on the heating unit's power output.
  2. Another alternative is to install a common wire transformer. This involves adding a transformer to your heating system to provide power specifically for the C wire. The transformer is typically connected to a power source and then wired to the C terminal on both the heating unit and the thermostat. This solution can help ensure a stable power supply for the thermostat.

 

It's important to note that implementing these alternatives may require some electrical knowledge and potentially working with high voltage. If you're not comfortable with electrical work or are unsure about the compatibility of your heating system, it's recommended to consult with a professional HVAC technician or an electrician. They can assess your system, recommend the best solution, and ensure that the installation is done safely and correctly.

 

Let us know how it goes.

 

Best,

Zoe

Mudfoots
Community Member

Thanks Zoe,

I have been looking all over for the power requirements for the nest thermostat and could not find anything specific.  It is getting about 3.5v from the c wire as it sits, but until I know the power requirements, I will not know how to properly proceed.  I have the c-wire adapter already installed, so my thoughts is that because this is an older house (1800's draaaaaaafty) that the unit simply runs for a while, drains the power, and sets off the message and I should just ignore it and focus on insulation issues...hahahahaha!

Cheers,

Tony

zoeuvre
Community Specialist
Community Specialist

Hi there, 

 

Thanks for getting back to us. The Nest Thermostat typically requires a 24V AC power supply to operate properly. It's important to note that the C-wire (common wire) is intended to provide a continuous 24V AC power supply to the thermostat, ensuring its stable operation and preventing power drain issues.

 

If your Nest Thermostat is currently receiving only around 3.5V from the C-wire, it's likely not receiving enough power to function correctly. This can result in various issues, including intermittent operation, error messages, or unexpected shutdowns. Could you list down the power readings of your thermostat's VIN, IIN, PS-* under Settings > Equipment > Power Info so I can take a closer look? 

 

Regards,

Zoe

Mudfoots
Community Member

VIN:33.064V  LIN :385(w) PS: W0385, WP-24

It had a error on it when I woke it to get that info; but the error was a weblink that disappeared, so it was useless.  Ran a power test, all good.  Battery says good as well.

Thanks for your help!

zoeuvre
Community Specialist
Community Specialist

Hello Mudfoots, 

 

Awesome! I'm glad that everything has been sorted out. If you have questions or concerns in the future, feel free to start a new thread, and we'll be happy to help.

 

Thanks,

Zoe