Article Summary:
The Nest Thermostat has a rechargeable battery that gets its charge directly through your heating or cooling system wires. If the battery level gets too low, the Nest Thermostat will shut down until the battery is recharged. A blinking red light indicates that it is charging and will eventually turn on.

Under normal conditions, the Nest Thermostat charges its battery from the low voltage wires on your heating and cooling system. However, there are several issues that can drain the battery:

• The battery drained during shipping
• There is a problem with the thermostat wiring
• There was a power outage in your home
• Your heating or cooling system isn't working properly (for example, clogged filters)

Whatever the cause, the Nest Thermostat will take steps to preserve battery charge as much as possible. If the battery charge is too low, the thermostat will first turn off Wi-Fi to help maintain heating and cooling control. In this case, your thermostat will show OFFLINE in the app, but you'll still be able to heat or cool your home by setting the temperature on the thermostat and your schedule will still be active.

If the battery drains below 3.6 volts, the Nest Thermostat will shut down — so you won't be able to control your heating or cooling with the thermostat or the Nest app. In this case, the Nest Thermostat's screen will be dark and unresponsive. It won't turn on when you approach, and turning the thermostat ring won't change the temperature. If the battery drains completely, the Nest Thermostat will still remember all your settings, so you won't have to go through setup or teach it again.

If you see a red light blinking light, this means the thermostat is receiving power but doesn't have enough battery charge to turn on. Once it recharges, it will automatically turn on and resume normal operation. While it's charging, you won't be able to control your heating and cooling system, but you can speed up charging by removing the display and connecting it to a USB cable.

Here are some troubleshooting tips for common scenarios that cause battery drain:

The battery drained during shipping

Your Nest Thermostat comes charged and ready to install right out of the box. However, in some rare cases, it's possible that the battery drained during shipping. If your thermostat doesn't turn on and begin setup a few seconds after you've connected it to your heating or cooling system, it's possible that the battery is drained.

As long as you see a blinking red light, you'll know that it's charging and should eventually turn on and begin setup. If you don't see a blinking red light, there may be other issues.

Troubleshooting Nest Thermostat power issues >

The Nest Thermostat will usually take about half an hour to recharge. But if the battery is very low, it can take as long as two hours. If you're in a hurry, you can remove the display and plug it into a USB cable to charge it faster.

Charging your Nest Thermostat using USB >

There is a wiring problem

Wiring issues usually occur when you're first installing a Nest Thermostat. However, they can crop up later as well, but usually for different reasons.

If you're installing a new Nest Thermostat, incorrect wiring can prevent it from charging. Double check that you have inserted the right wires into the right connectors. Also check that they are fully inserted and that they are making solid contact with the connectors. The connector button should stay down if the wire is fully inserted as shown in the picture here. The following articles have more troubleshooting tips for power and wiring problems after installation.

My Nest Thermostat won't turn on after installation >

My Nest Thermostat can't detect installed wires >

If you have an older heating or cooling system, the wiring may be faulty or damaged. In this case, it's best to have a professional HVAC installer help you. Nest Certified Pros have advanced training to solve issues with systems controlled by Nest Thermostats. You can contact a trained professional in your area with our Nest Pro finder.

There was an extended blackout

Your Nest Thermostat's battery has enough capacity to keep working during short power outages that last an hour or two. However, it may not be able to turn back on immediately after a longer blackout.

When the power comes back on, you should see a blinking red light indicating that it's charging and should eventually turn on. In rare cases, surge damage may occur when the power is suddenly turned back on by the power company. If your Nest Thermostat isn't charging after power has been restored to your home, check your breaker box to see that all switches are in the ON position. If you have fuses, make sure none have been blown and need replacing. Also check that your heating or cooling system is receiving power. It may have a fuse that needs to be replaced. In this case, you should contact a local Nest Pro for servicing. If everything seems to be working correctly, you can pull off the Nest display and charge it with a Micro USB cable.

There are other heating and cooling system issues

In addition, issues with your heating or cooling system can also drain the battery. For example, a clogged filter can cause your system to overheat and automatically shut off. When this happens, your Nest Thermostat can't draw power from your system to charge its battery, and it may drain so much that it has to shut down. You may also see a Furnace Heads-Up message on the thermostat screen, in your Nest app messages, or in your monthly Home Report email.

Even if you are able to restart your system, repeated automatic shutdowns will eventually drain the Nest Thermostat battery. If you're experiencing these symptoms, check your system's air filters and replace them if necessary, or contact a local Nest Pro to replace them for you.

There are a wide variety of issues that may affect your heating and cooling system depending on its type and age, and what kind of climate you live in. But we're here to help. Contact our Support Team any time if you're experiencing issues with your heating or cooling system.