No Power to Nest Thermostat

hand touching digital thermostat with leaf and eco icons

It's a frustrating experience when your thermostat isn't working because this is really the hub of the home. Having no power to Nest thermostat systems might mean that you end up being incredibly uncomfortable because you can't regulate the temperature, which sort of defeats the whole purpose of having a house.

The No Power Alert

Are you getting a "no power" alert? There are a couple of reasons why this might be happening.


Sometimes, the thermostat's wiring has shorted out or disconnected or there is another wiring problem that is keeping the thermostat from receiving signals. The system connects to the thermostat with a C wire, also known as a common wire.


The problem might not be with the thermostat. The first troubleshooting step you should take is to go check your fuse box.

Check the circuit breaker to make sure nothing has tripped and check to make sure no fuses have burned out, as this will affect the power supply inside your home. You should also make sure the outlet is receiving power by plugging a device into it and testing to see if the device turns on.


It's one of those solutions that's so simple, you could take two days just to figure it out. Often, it's human nature to look for big problems when something isn't working correctly, especially a piece of technology like your thermostat.

But sometimes, it’s just that the battery is low. Change the batteries to see if this might fix the problem before you do more serious troubleshooting.


If the obvious issues aren't at play and doing the simple stuff doesn't get the thermostat working, it's time to try some more serious troubleshooting.

Check the Menu

Start by tapping the touch bar to engage the thermostat. Tap it again to open up the menu.

Select settings and then slide the touch bar to open the equipment menu. This is where you should see the "no power" alert right on the screen, or perhaps a numerical error code.

Look at the Wiring

Go back to your settings menu and check the equipment menu again for your next troubleshooting step. Look at the "wiring info" menu. This will bring up a little diagram showing you the wiring in the thermostat system.

If any of these wires appear in a gray color on the diagram, the wire is not sending voltage to your thermostat. If all the wires are gray, the system itself is not being powered.

If a single or a couple of wires are gray, check the system app to make sure that each one is entered properly in the app. Before you do this, however, make sure you turn off the thermostat to prevent any damage.

The power switch for the thermostat is in the circuit breaker, fuse box, or system switch. The system switch might look like a standard light switch, usually in the utility area of the home.

Pull the thermostat away from the base and remove it. Check each wire to ensure it is correctly identified.

Disconnect each wire by pushing down on the connector tab and gently, gently, pulling out the wire. Straighten each wire end, strip it to expose 1/3 to 1/2 inch of copper if this is not already the case, and then secure the wire to its proper connector.

Once every wire has been re-connected, re-attach the thermostat to the base and turn the power back on. Wait a few moments and then check the equipment menu again to take another look at the wires and see if the diagram now appears to be normal.

Try a Nest Power Connector

Your thermostat might need a Nest power connector in order to receive enough power. This problem may also be resolved with a C wire.

First, check for a spare C wire. If you find one, connect it to the C connector on the thermostat. If you don't have this C wire, install a Nest power connector or hire an electrician to install a new C wire for you and connect it to the thermostat.

Troubleshooting an E74 Error

You might be getting an E74 error message, or possibly N72. This usually means you're having a problem with the Rh wire.

This error code means the Rh wire isn't receiving any power. The Rh wire is a red wire that is supposed to supply constant power.


Try unplugging your thermostat and then plugging it back in to see if the wire starts to receive power. Leave the device unplugged for at least one minute before turning it back on.


If you're still having trouble with getting no power to Nest thermostat systems, clean out the drain pipes.

Drain pipes can become clogged if the thermostat is in an area of the house with a lot of humidity. You can find this around the kitchen and bathroom areas.

A small sink snake should be sufficient to clean out the drains and this should remove any clogs if one is present. Gently and slowly push the snake through the drain line to remove clogs.

Check the Condensate Float

You should also make sure the condensate float switch is working properly. First, find this switch and lift it up to remove it from the PVC pipe.

Look for the float which should move freely up and down. If you can't easily make it move, you might need a new switch.

If the switch moves freely, move it out of the way and use a flashlight to examine the drain pipe. If you see any debris in there, this could be causing the problem.

Test the drain line by pouring a cup of water ad see if the liquid disappears. If it does not, you have a clog.

Clean this drain line with a cotton swab or pipe cleaner, as this is a very small line. Pour a little vinegar, about one cup, into the pipe.

The vinegar will break up hard water and debris that could be clogging the line. Do not use a drain cleaner, as this can eat through pipes and cause you much bigger problems.

If this doesn't treat the clog, a weed trimmer line can be gently pushed into the drain to work as a thin snake. Use this only as a last resort.

Check the Rc Wire

Turn off all breakers to the HVAC system. Make sure the entire system is off.

Detach the thermostat from the base to expose the wires. Without touching the other wires, disconnect the Rc wire.

Look over the wire carefully. It should have copper exposed at one end and this copper should not be bent.

The wire should not have paint or corrosion on it. Clean it off gently if you find this and remove any debris or dirt.

Use a voltmeter to test the wire and see if the voltage is consistent through the length of the wire. The voltage should read 24 VAC.

Insert the wire into the Nest connector, making sure the connector button stays down while you do so.

Turn the breakers back on and let the system power back up. Go check the thermostat to see if the problem is resolved.

Check the Air Filter

Your HVAC system has an air filter, which is usually concealed by a grate that's not so easy to reach, such as high on the wall. It may also be inside the furnace itself, which means you will have to turn the power to the system off before you check the filter.

Visually inspect the filter to see if it is dirty. If so, replace it.

The air filter should be replaced every 30 to 90 days to keep proper airflow circulating through the system. A dirty air filter impedes airflow, which can cause your HVAC system to stop working perfectly.

What Do the Codes Mean?

There are many different error codes that may be displayed on the screen. Sometimes, these codes will provide very little information.

Other times, the code can give you a good idea of what exactly is going on with your thermostat. There are a few codes that relate directly to power levels, or lack thereof, for your thermostat.


Often, this code indicates that the thermostat is receiving too much power. This can actually be dangerous and you should not attempt to do any service on your thermostat until you can hire a professional electrician to check for bad connections and other problems that could be causing this dangerous error.

Do not attempt to fix this problem yourself unless you are a professional electrician.


This error usually appears when it's incredibly hot outside, when your AC unit has been working hard to keep up. This means that not only is the system not receiving power, but the backup battery is also depleted, too.

In a pinch, you can always supply power to the thermostat with a USB cable. This will provide some much-needed power if the demands on the HVAC system are particularly high.


When you see this error, there is a problem with the wiring. Often, this is a problem along the R wire.

Check all the wires, re-connect them, and see if this resolves the issue. Always turn the power off to the thermostat before you do any work on the wiring.


You will see this code when the system is disconnected from a power source. When this error happens, the thermostat will start to use the backup battery system.


If you see this error, your thermostat needs a C wire or a Nest power connector.

No Power to Nest Thermostat?

There are lots of things that could go wrong and cause your Nest thermostat to lose power. After you look at the error codes and perform troubleshooting to try to pinpoint and fix the problem, you will need to get additional help if the problem remains.

Most of the time, you will be able to troubleshoot and fix problems with your Nest system yourself. If this doesn't work, however, you can always contact Nest support or consult with a professional electrician.

Nest Thermostat FAQs

Are you using the right Nest thermostat?

Is your Nest thermostat compatible with your home? There are different power levels of Nest thermostats and different models you should use based on your property's infrastructure.

To make sure you're working with the right thermostat, check online. Nest has a compatibility checker that's easy to use so you can check compatibility and get the right model of thermostat as needed.

What's the first step when there is no power to a Nest thermostat?

when you first notice that your thermostat is not getting power, check to make sure it is turned on and then check the battery. Look to the breakers next to see if one has tripped.

Once all the simple steps are completed, look at the error code and try to see what the error is if you have a specific code, rather than a generic power error code.

Once you confirm that the problem is not easily solved, it's time to start your troubleshooting steps to find and address the issue that's keeping your Nest thermostat from getting power.

What's the benefit of a Nest thermostat?

Nest thermostats are programmable but they do a lot more than that. The system monitors your energy usage and provides daily reports to make it easier to save energy and keep the system running efficiently.

This energy efficiency lowers the cost of your utility bill, which is never a bad thing. If your thermostat isn't working properly, troubleshoot it and fix the problem as soon as you can rather than letting it wait, as this will cost you more money on bills.

Further Reading

4 Things to Know About Smart Thermostats

How to Calibrate Thermostat Temperature

How to Install a Wireless Thermostat

How to Replace Your Thermostat

Programmable and Automatic Thermostats

Replacing Carrier Thermostat with Nest

Troubleshooting AC Thermostat

Troubleshooting Electronic Thermostat Problems

What to Know When Buying a Thermostat

Wiring a New Thermostat