How To Fix It

Why Nest Thermostat Not Turning On? How To Troubleshoot It?

A Nest thermostat is a smart device that lets you control the temperature in your home to save time and money. Sometimes, it can be prone to problems, such as when it won’t turn on. Why does this happen? 

Common reasons for the Nest thermostat not turning on include a faulty power supply, circuit breaker issues, loose display, a dirty unit, incompatibility, and low brightness. To fix the issue, try replacing the battery, aligning the display and base, and cleaning the thermostat regularly. 

In this article, I’ll talk about the most common reasons why your Nest thermostat isn’t turning on. More importantly, I’ll discuss the best solutions. 

1. Faulty Power Supply 

Your Nest thermostat has two primary power sources, which are necessary for the device to operate. 

One of its power sources is the two standard alkaline batteries. The AAA batteries work as a backup. They also supplement the power if the system cannot deliver enough. While it’s a crucial component for running the thermostat, it’s not the main power supply. 

However, the batteries might be due for a replacement if you’ve used the thermostat for a while. 

In addition, the thermostat also uses power from the common wire. The wire connects the thermostat to your HVAC system. It does not only allow the system to run, but it also charges the battery. 

The device won’t turn on when the thermostat runs out of battery or the power supply is cut. You’ll get a notification when the battery is low, but you might miss it if you’re not paying attention. 

Aside from not turning on, a faulty power supply can also be why your thermostat turns off by itself

Read: How Does Nest Temperature Sensor Work?

How To Fix?

An easy solution to this issue is to change the battery. Here’s a quick step-by-step guide to replacing the batteries

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  1. Take the display out of the base. 
  2. Remove the old batteries from the back of the thermostat. 
  3. Insert two AAA alkaline batteries. 
  4. Return the device. 

You might also need to charge the unit. Depending on the model, it can be compatible with a USB or micro-USB port. You can charge it directly on a wall charger or your computer

Meanwhile, if the issue is the common wire, you might need to install a Nest Power Connector. Ensure a tight connection for the system to work. Loose wiring can also result in a faulty power supply, so you should check the connections. 

Do you need help with how to install a power connector? Watch the short video on YouTube and learn how to do it. 

2. Issue With the Circuit Breaker 

The circuit breaker is a home safety feature that protects against electrical shock, fire, and property damage. It trips when it detects a change in electrical flow. Hence, the circuit breaker can deactivate everything that connects to it, including the Nest thermostat. 

An easy way to tell if the circuit breaker is the cause of the problem is to look at the other appliances it powers. If these appliances are working, the circuit breaker isn’t the culprit. 

How To Fix?

Resetting the circuit breaker can solve this problem. Turn the switch off and turn it on again. Be careful when working with the circuit breaker, as it can cause electrical shock. Consider wearing gloves for your safety. 

If resetting it does not work, you might need a replacement. It can be a more complicated job, so it’s best to call an electrician to replace the circuit breaker.

Read: Why Nest Thermostat Not Following Schedule? 

3. Loose Display 

Some thermostat issues are simple. Nothing can be wrong with the system itself, but the problem can be with the installation. The display can loosen from the base over time, and this can prevent the unit from turning on

The display must sit fully on the base for the thermostat to turn on. Otherwise, it will not receive a power supply, and the battery will not charge. The display can easily loosen from the base of the thermostat if it is in a part of your house with high foot traffic where people can bump into the unit.

If the battery is charging, a red light blinks on the unit. It means that the display is in the proper position. Hence, you should look for other potential causes. 

Read: Why Nest Thermostat Showing Wrong Temperature? – Troubleshooting Guide

How To Fix?

Check the position of the thermostat against the base. Check the cables at the back of the unit. None should be sticking out. Otherwise, this can prevent the unit from having a snug fit to the base. Align the display and base connectors for the system to turn on. 

4. Dirty Thermostat 

Dirt can accumulate in the thermostat over time. The unit can get dusty, which can be the culprit for some problems. Among others, one issue you might encounter is that the unit won’t turn on. It might not be as common as the others on the list, but it’s one thing worth looking at. 

Aside from not turning on, dirt can also make the Nest thermostat inaccurate. Hence, you can’t take advantage of its full features. 

How To Fix?

Cleaning your Nest thermostat is a must. It’s a quick and straightforward process, which you can complete by doing the following:

  1. Lightly spray water on a soft and clean cloth
  2. Wring the cloth to remove excess moisture
  3. Wipe the face and side of the thermostat. Do this carefully, making sure no drops of water will get in. 
  4. Take the display out of the base. Use a brush with soft bristles to clean the back of the unit. 

Read: Which Saves More Money: Ecobee Or Nest?

5. Incompatibility With the System 

The issue can also be technical. For instance, your Nest thermostat may be incompatible with the heating system you want to connect. Hence, the thermostat may not receive power and won’t turn on. 

Below are some systems that will not work with a Nest thermostat.

  • High-voltage systems: These include electric-powered baseboard heaters and other radiant systems. You can often find them built on the wall. 
  • Millivolt heaters: They include floor and wall heaters using electricity or natural gas as the power source. Because they’re primarily low-voltage systems, the power may be insufficient for Nest thermostats. 
  • Solid fuel systems: If your heating system uses biomass materials, such as wood chips and coal, the thermostat will not work. 

How To Fix?

Ensure compatibility between the Nest thermostat and your HVAC system. If it falls within the above categories, expect that the power won’t be enough, so the system will not turn on. You might need another kind of thermostat for different heating and cooling systems. 

6. Low Brightness 

If you’re a first-time Nest user, you might think that the thermostat isn’t turning on, but the truth is, the problem is simply the brightness. Newer models no longer have the option to adjust the brightness manually. You can choose Auto, Low, Medium, and High brightness levels in older models. 

How To Fix?

The solution depends on the model you’re using. Some will give you the freedom to change the brightness. However, users reported that the only thing they did was direct a flashlight on the thermostat to increase its visibility whenever they needed to change a setting. 


It’s frustrating when the Nest thermostat won’t turn on, especially when you need it the most. The issue could be as simple as the low brightness of the display or a loose base. It can also signify a faulty power supply, which means you must change the batteries or check the connectors.