Nest Thermostat Blinking Red? (Here's What You Can Do)

Nest is famous for its learning technology. Its sole purpose is to learn your routine so you don’t have to worry about programming it. We as users are at a disadvantage when it comes to learning about our Nest. After all, we have many more things in our brains than just the workings of our thermostat.

When our Nest does something out of the ordinary, we don’t always know what it means. Blinking lights—especially blinking red lights—seem cause for alarm. But not to worry.

If your Nest thermostat is blinking red, it means the battery is running low. The light should disappear when the battery is fully charged. You can charge it yourself by disconnecting Nest from the wall and plugging it into the USB cable it came with. For a more permanent solution, install a C wire or plug Nest directly into a wall outlet.

There are a few ways Nest thermostats can receive power. The most commonly suggested way from Google is to power the thermostat with your HVAC system.

Typically, smart thermostats require a C wire in order to receive constant power. Nest says you don’t need one for their thermostat. However, many users find a C wire beneficial and end up installing it if they don’t already have one.

The last option to power your Nest is to plug it into a wall socket. For this, you need to use the power cable and plug that came with the device. Nest should be installed on a wall that’s close to a power socket to ensure the cord will reach.

You may choose to install your Nest without a C wire. In this case, the R wire which powers your HVAC system will also power your Nest.

Each time your HVAC system kicks on, the Nest battery receives a charge from the R cable. The downside to this power method is that Nest only receives power when the system is running. The rest of the time, Nest relies on its battery. (More on this later.)

Note: If you have more than one R wire, do not be alarmed. The Rc wire powers the air conditioner while the Rh wire powers the furnace. If you have one but not the other, it powers both heating and cooling and can be put into either R terminal on your Nest.

Most HVAC systems don’t put out enough power to constantly charge a smart thermostat. The sole purpose of a C wire is to give the thermostat a constant charge, whether or not your HVAC system is running. Because smart thermostats are connected to Wi-Fi, they need to receive power at all times.

So why does Nest maintain that you don’t need a C wire?

Well, technically, you don’t. Nest will still run without one. But as mentioned above, it only receives power when the HVAC system is running. Each time a heating or cooling cycle ends, the system shuts down and the Nest battery is left on its own.

If you have your HVAC system off long enough, the Nest battery can drain down completely, resulting in a blinking red light.

If you choose to use your Nest without a C wire, you can remove it from the wall and charge the battery yourself. When you pull off the thermostat display, you’ll notice a USB port on the back. This is true for 1st, 2nd, and 3rd Generations as well as the Nest E, though the 1st Generation has a mini-USB port.

Using the cable and plug provided, plug the thermostat into the wall to charge. You can also opt to plug the thermostat into your computer. In this case, use only the cable.

You’ll know your Nest is charging when you see a blinking light. The color changes depending on the level of the battery’s charge. It takes roughly 30 minutes to charge Nest completely. If the battery has been completely drained, it may take up to 2 hours.

Once it’s fully charged, replace the thermostat display back on the wall.

The downside to manually charging your Nest’s battery is that your HVAC cannot be used during that time.

The final solution to charge your Nest and get rid of the blinking red light is to permanently plug it into an outlet. As with the C wire, this solution ensures a constant charge to the battery.

However, there are a few downsides. The Nest needs to be installed on a wall near an outlet in a highly trafficked area for maximum energy efficiency. Not to mention, you’ll have an unsightly wire dangling at all times. This doesn’t provide a very clean look to the otherwise sleek design on the Nest.

Related Questions

How long does Nest’s battery last?

Nest’s battery lasts for up to 2 hours. With the intermittently charging it receives from the HVAC system, you may not notice the battery draining for a few months. However, that length of time depends on how often you run your system.

Why is my Nest blinking green?

A blinking green light on a Nest means it’s automatically updating its software. You’ll notice the display restart during this update. This should only take 1-2 minutes. If it takes longer, check to make sure the thermostat is completely connected to the base. Occasionally, you may have to restart your Nest.

If your Nest thermostat is blinking red, it’s nothing to be concerned about. It simply means the battery is low. You can avoid this blinking red light forever by installing a C wire to give constant power to the thermostat. You can also choose to plug it into a wall outlet.

Manually charging the battery is another option. For this, the Nest display needs to be removed from the wall and plugged into the USB cable provided. Please note that your HVAC remains inactive during a manual battery charge. The blinking red light will disappear until the battery drains again.