The voltage and current values on your Nest thermostat help you gauge the battery levels and how much power the device is consuming at any given time.
Ideally, you want your battery voltage to be higher than 3.7V and input current greater than 20mA.
If these values dip, you might have to troubleshoot, so keep reading to learn more.
How to Access the Power Information Menu
In the power settings menu you’ll have four different readings:
- Battery Voltage
- Voc (Open Circuit Voltage)
- Vin (Input Voltage)
- Iin (Input Current)
To Access These Values on your Nest Thermostat and Nest App:
- Open the Nest app or wake up the thermostat by pressing the ring button
- Cycle to “Settings” and press the ring button to enter
- Circle all the way down to “Technical Info” or “Device Information.” Enter this menu
- Tap on “Power.”
On your Google Home App:
- Open the Google Home App
- Tap and hold your device’s tile
- Then, tap on “Settings” from the small drop-down list that shows up
- After that, tap on “Device Information” from the menu options
What is the Ideal Nest Thermostat Battery Voltage?
When it comes to the Nest thermostat battery voltage, 3.7V or higher implies the battery is sufficiently charged and allows the thermostat to function without any restrictions.
Maintaining the battery voltage at this level ensures the device can provide optional features such as remote control through Wi-Fi, software updates, and motion sensing.
However, when the battery voltage falls below 3.6V, the Nest thermostat goes into a power-saving mode to prolong its battery lifespan.
In this low-power mode, these optional features are disabled and it will only help manage your home’s temperature.
So to avoid any inconvenience, it's important you monitor the battery voltage of your Nest thermostat regularly and ensure it stays above 3.6V.
What's the Ideal Voc, Vin & Iin Voltage on a Nest Thermostat?
The Voc, Vin, and Iin indicate the flow of electricity through your thermostat wiring. These are equally important and you need to monitor them so they won't go below a certain level.
- For Voc, Google recommends you keep it between the range of 29V-42V.
- For Vin, 29V-42V is ideal when you have a C-wire connected.
- If you don’t have a C-wire, Vin should be 29-42V when the HVAC system is not running
- When the system is running, Vin must read 6-7V (without the C-wire).
- For Iin, 100mA-200mA is best when a C-wire is connected.
- Without a C-wire, 20mA-40mA for Iin is enough.
Anything lower than that could imply an issue with your battery, wiring, or internal components.
So be prepared to troubleshoot and if you haven’t done already, consider setting up a C-wire for better power stability.
At SmartHomePerfected we always advise readers not to undertake any work they are not competent in performing and if in any doubt, it is best to seek the assistance of a professional.
Troubleshoot Low Battery Issues and Blank Screen on a Nest Thermostat
In most situations where you're troubleshooting the Nest thermostat, whether that's connectivity issues, low battery errors, or a blank screen, measuring the system voltage is a crucial step.
If the power levels in your thermostat wiring or battery are too low, the thermostat will disable certain functions or stop responding altogether.
So when troubleshooting these issues, you will most likely have to carry out the following practices:
- Check power information via the menu
- Check the thermostat wiring strip for low voltage (using a multimeter)
- Replace or Recharge the battery on your thermostat
- Check your C-wire connection or install a C-wire if you don't have one.
I've already shown you how to carry out the first step of this troubleshooting procedure, so let's talk more about how to carry on with the rest of the steps, especially if you can't access the thermostat menu.
How to Check Voltage With a Multimeter
If you're having issues with battery voltage, you will need to confirm the correct voltage is through the R wire and out the W, Y, or C wires.
This requires you to remove the thermostat from the wall mount and insert multimeter probes into live wires, so make sure you take the necessary precautions or get help from a professional.
To check the voltage on your thermostat wiring strip:
- Carefully pull out your Nest thermostat from its base plate.
- Configure your voltmeter to the AC voltage (ṽ) mode,
- If your multimeter doesn’t have the auto range function, choose an AC voltage range that’s higher than 24V. (Usually, the available option is 200V.)
- After that, hold the red probe on the red wire or Rh-terminal.
- As you maintain the red probe's position, keep using the black probe to measure voltages on the other non-red wires or terminals.
- Usually, the voltage should measure 24-28V if a specific wire is energized. So if the fan is on, the “G” wire (typically green) should measure 24-28V.
- Also if you have a C-wire make sure the voltage between Rh/Rc and C falls under this range. If this voltage is lower than 24V (say 8V) it might indicate the system is not getting enough power.
If you are uncertain or encounter issues during the testing process, do not hesitate to reach out to a professional technician.
They will be able to assess and diagnose any inconsistencies in voltage, faulty wiring, and other electrical concerns that could be causing problems with your equipment.
Replace or Recharge Thermostat Batteries
In case your thermostat runs entirely on batteries, you must make sure the battery is fully charged.
Depending on the model, you will have to replace the batteries or recharge them using a Mini-USB or Micro-USB cable. Make sure to let it charge for a good couple of hours before plugging it back in.
Supplementing your Thermostat with a C-Wire
If you're already running your nest thermostat on batteries and you're constantly experiencing low voltage errors, it might be best to install a C-wire into your thermostat.
A C-wire will help supplement your thermostat with a steady source of power and provide more stability to the system. Even Google recommends you install a C-wire on the app.
There are several methods to provide a C-wire into your system. You can either:
- Hardwire a C wire into your existing thermostat wiring strip
- Install a C-wire Adapter or Transformer
- Reuse your G Wire as the C wire
Hardwire a C-Wire
The task of installing a C-Wire is complicated, especially when you have to draw the new thermostat cable from your HVAC system to your thermostat and hide them.
So depending on your circumstances and skill level, this can easily turn into a big DIY project. Instead, I recommend enlisting the help of a professional or checking out the alternatives mentioned below for a quick fix.
Install a C-Wire Adapter
This would be your next option if you don’t have a C-wire, or laying a cable seems too impractical at the moment.
There are a few devices that can help set up a virtual C-wire in your system.
Whatever method you choose, you will have to do a bit of electrical DIY, so make sure to prepare your tools and plan out how you're going to lay out the cables for this new wiring system.
In terms of the tools necessary, you would typically need a
- Philp’s head/flathead screwdriver: To reconnect the terminals
- Cordless drill: To mount the adapter closer to the control board
- Appropriate fasteners: zip screws to fix the adapter to the metal sheet on your control board
- Double-sided tape: If you want to just stick the adapter without any drilling
- Spirit Level: To keep things straight and square
- Wire Strippers: To cut wires and strip them to make splice connections
- Wire Nuts/Splice Connectors: When you need to splice the wires between the adapter and thermostat
- Smartphone or Camera: To take a photo of the existing thermostat wiring configuration
- (Optional) Label Maker: To label the thermostat wires
- (Optional) Non Contact Voltage Tester: To ensure the wires are safe to handle
Reuse your G Wire as a C Wire
If you're looking for a way to power your Nest thermostat without using a C-wire or adapter, repurposing your G-wire can be the only solution.
Keep in mind that by using the G-wire as a C-wire, you'll lose fan control features such as independent or “fan-only” mode, as the G-wire is normally responsible for these functions.
Additionally, if your HVAC system includes a zoning panel, this method may not work efficiently due to compatibility issues.
So here’s the process:
- First, turn off the power to your thermostat and HVAC system. Locate the appropriate breakers and disconnect switches and turn them off.
- After that, remove the Nest thermostat from the wall mount.
- Take a picture of the existing wiring configuration.
- Locate the green G-wire in your thermostat's wiring and connect it to the C-terminal at both the thermostat and furnace ends.
- Then, head over to the furnace control board where the other end of the thermostat wiring strip connects to the rest of the HVAC system.
- After making sure the entire system is switched off, look for the terminals which connect the thermostat wiring strip
- Here, disconnect the green-colored G wire and connect it to the C terminal, just like you did on the thermostat side. Don't alter any other wire connections.
- Using a small jumper wire, connect the now-empty G terminal to the Y (Cooling) terminal on the control board
- Restore power and see if the thermostat detects the C-wire
Your thermostat will now function with a C-wire but since you’ve shorted the G terminal with the Y terminal, the blower fan will only turn on when the cooling system kicks in.
Monitoring the power information on your Nest thermostat is crucial if you want to ensure the device has enough power to maintain all its functions.
Usually, you want the battery voltage to hover around 3.7V for optimal operation. Anything lower than that, and you might lose certain functions such as Wi-Fi connectivity and motion sensing.