ToolCrowd is reader-supported. When you buy through links on our site, we may earn an affiliate commission. Learn more

How Does a Nest Thermostat Get Power?

In a world where we rely so heavily on technology day-in-day-out, it’s no surprise that smart thermostats are one of the most sought after gadgets for the home.

Now owned by Google, the Nest Thermostat is one of the most popular smart thermostats on the market.

The handy devices allow you to control the temperature within your home from anywhere in the world, providing you with optimum convenience and helping you save on energy consumption while you’re at it.

This article covers how the Nest Thermostat gets power, including whether it is battery-powered or if you need to plug it in.

The Nest Thermostat must be plugged into mains power or wired into a heating system’s power supply to function. Without a constant power supply, it won’t be able to control a home’s HVAC systems. It does have a built-in battery to cover power outages, but this won’t continuously run the device.

Read on to find out more about how the Nest Thermostat gets power, how long the battery will last without a constant power supply, and how to charge the battery after it is fully drained.

How Does a Nest Thermostat Get Power?

Nest Thermostats get their power from your home’s HVAC system via two wires — the C wire and the call-for-heat wire, also known as the R wire.

Alternatively, you can plug the device into a power socket using the power cable and plug included in the box. If you are using this method, ensure you install your thermostat close enough to a plug socket for the cable to reach, as you shouldn’t move the device once it’s on the wall.

If you’re replacing an existing thermostat, you’ll be able to hook your Nest up to the existing cables. Alternatively, if you are installing your Nest Thermostat in a new location, you’ll need to make sure it is close enough to a power socket that you can plug it in with the cable and plug provided.

When used in Europe, Nest Thermostats also rely on a stable connection with Heat Link, which is a device that connects to the heating system and interprets the information between the boiler and the thermostat.


Nest Thermostats made for North America do not use Heat Link. If you’re located in the United States, you do not need to worry about this additional requirement.

Your Nest Thermostat needs to communicate wirelessly with Heat Link, so make sure it is no less than 30m away.

When connecting up the Heat Link, you’ll need to locate the call-for-heat circuit in the heating system. This could either pass through a junction box or be connected directly to the boiler’s control circuit.

Like the Nest Thermostat, the Heat Link also requires power, so you’ll need to connect the live and neutral connectors to the boiler or junction box.

Remember to install the Heat Link before installing the Nest Thermostat; otherwise, the high voltage current will cause significant damage to your smart home device.

The final stage in the installation process is to connect the C wire and call-for-heat wire from the Heat Link to the Nest Thermostat, which will act as the constant power source for the device.

Once hooked up to a power supply, you’ll be able to control your home’s heating and cooling systems via the Nest Thermostat device.

an image from an article about how the nest thermostat gets power showing the nest app being used on a smartphone


You don’t need WiFi to use the Nest Thermostat, but WiFi is required to control Nest from the Nest app via a smartphone or tablet device as shown above.

Does a Nest Thermostat Need to Be Plugged In?

Nest Thermostats must be connected to the HVAC system via a C wire and R wire to receive a constant supply of power.

If this power supply were to cut out, for example, during a power cut or the HVAC system failed, a backup battery would keep the Nest Thermostat operating for a short amount of time.

After one to two hours, the batteries will run out of power and cause the smart thermostat to shut down completely. It will only power up again if the battery is charged or the power supply from the HVAC system is reinstated.

Does the Nest Thermostat Need to Be Hardwired?

The Nest Thermostat will need to be hardwired into your home’s HVAC system and power supply to operate to its full potential.

You can achieve this by using the relevant cables to physically connect them or using a Heat Link connection (in Europe only; see above) to link the thermostat with your home’s heating system wirelessly.

There are two options for plugging in a Nest Thermostat:

  1. Plugging it into the mains supply through a socket located close to the device.
  2. Hardwiring it to wherever the previous thermostat was installed.

One last thing to note is that the Nest Thermostat is designed to stay in one place, so you should carefully consider where you put it before you install your smart home device.

Can You Use a Nest Thermostat Without Power?

Whilst the Nest Thermostat does require a constant supply of power to be able to run day-to-day, you may be wondering what would happen in the event of a power cut.

Luckily, this smart thermostat has a built-in battery that will keep the device in operation for a limited time.

This rechargeable lithium-ion battery will keep running for one to two hours during a power outage before it shuts down altogether.

One thing to note is that once it runs off the battery, the Nest Thermostat will no longer be ‘smart’ because it will have lost its connection to the HVAC system, and the WiFi will also be down.

When operating in battery mode, the thermostat will also automatically cut off many of the ‘smart’ functions to preserve power. For example, you will not be able to control the thermostat via the app on your smartphone or tablet whilst it is not connected to the power supply.

The Nest Thermostat’s battery is not suited for everyday or heavy use, so if you live in an area with frequent power outages, you cannot rely on the backup battery as a reliable power supply.

Once the battery runs out after one to two hours, the Nest Thermostat will shut down, and all its features will be cut off until a power supply has been re-established.

Is the Nest Thermostat Battery Powered?

The Nest Thermostat is powered primarily by your HVAC system. However, it also has built-in rechargeable lithium-ion batteries, which act as a backup power supply.

The battery power will only kick in when the power supply from the HVAC system has been cut off, for example, during a power outage or if a fuse blows.

The thermostat will continue to operate on basic functions until the power supply is established again.

How Long Does a Nest Thermostat Battery Last?

If your HVAC system is turned off or there is a power cut, the Nest Thermostat’s battery will keep the device working for another one or two hours.

Once the power supply has been reinstated, the power from the HVAC system will begin recharging the batteries. The device will take approximately 2-3 hours to become fully charged again. 

Alternatively, you can charge the Nest Thermostat’s battery via the USB port in the back of the device.

How to Charge a Nest Thermostat Using a USB Cable

Here’s how to recharge your Nest Thermostat using a USB cable:

  1. Remove the Nest Thermostat from the wall.
  2. On the back, you will notice a USB port. Depending on the model you have, it will either be a micro USB or a mini USB port.
  3. Plug a USB cable into the Nest device and connect it to a wall plug socket, a battery power bank or a computer.
  4. Charge the Nest Thermostat for two to three hours. A flashing red light on the front of the thermostat will confirm if the battery is charging successfully.

What Is the C Wire?

The C wire, or ‘common wire‘, provides a constant flow of power from the HVAC system to the Nest Thermostat.

The R wire uses a transformer to provide power to the HVAC system, so it works in unison with the C wire to ensure the smart thermostat has a continuous flow of energy that will keep the display and WiFi functions running 24/7.

Why Is My Nest Thermostat Not Getting Power?

If your Nest Thermostat is unresponsive or won’t turn on, there is a chance it isn’t getting a power supply.

Whilst it does have a built-in battery installed, this only functions as a backup power source and is not strong enough to keep the thermostat going for long.

There are several reasons your Nest Thermostat is not getting power, for example, a blown fuse, power cut, damaged wires or incompatible power system.

You can remove the thermostat from its base and charge it by plugging a USB cable into the wall, battery pack or computer. After around 10 minutes, you’ll be able to turn the device on and manually restart it.

Once it has rebooted itself and the thermostat is still not connected to the power, you may have a power outage or a dodgy power cable connection.


Turn power to your system off at the system switch or fuse box. Doing so helps protect your system and thermostat from possible damage.

Take the device off the wall and makes sure the C wire and R wire aren’t out of place and are still connected correctly.

Also, try turning the breaker or switch that controls power to your HVAC system off and on again. Ensure the button is pushed fully to the On position.

Check the fuse controlling the power hasn’t blown; replace it if it has and turn it back on again.

If you still have issues getting power to your Nest Thermostat, we suggest you contact the Nest Support Team for further assistance and guidance.

In Summary

In a nutshell, the Nest Thermostat uses your home’s HVAC system to get a constant supply of power.

It also has a built-in battery that will keep the device powered for around two hours during power outages or if the heating system’s power isn’t working. However, the battery is only a backup power supply and shouldn’t be relied on as a permanent energy source.

If you enjoyed this article, you’ll probably enjoy the following, too:

toolcrowd expert writer profile image
Author: Tamsin Bright
Writer, ToolCrowd
Tamsin Bright regularly writes about architecture and home design topics and is the editor for the Smart Home and Home Tech sections of ToolCrowd. Tamsin holds a bachelor’s degree in Architecture and loves nothing more than helping people see the potential in their homes and making their lives easier through great design. When she’s not writing for ToolCrowd, you can find Tamsin indulging her passions for graphic design, cooking, gardening, and all things tech. Contact Tamsinarrow_right_alt