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A variety of factors such as software problems, hardware failures, or wiring complications may be causing your Nest thermostat to be unable to generate hot or cold air.

In this guide, I walk through 14 steps to fix this problem and get your HVAC system back under control.

Step 1: Manually Adjust the Temperature

If you've been controlling the Nest thermostat via the app, try adjusting the temperature manually at the thermostat itself. 

Try changing the temperature only by a couple of degrees higher or lower than the current ambient temperature and see if the heating or cooling equipment kicks in. 

This will help you rule out any connectivity issues between the mobile apps and also check the thermostat's condition. 

Step 2: Check For Any Error Codes

If that doesn’t bring the heating and cooling equipment back up and running, the next thing to do when your HVAC equipment doesn't turn on is to check the thermostat or mobile apps for any error codes or alert messages. 

Usually, the app would let you know immediately if something was wrong. Apart from that, it would also show instructions on how to fix the issue. 

Step 3: See If The Heating and Cooling Equipment Is Turned Off

If you didn't receive any error codes or alert messages, the next step would be to see if the heating equipment actually turns on. 

  • Depending on your system, you might be able to hear noise from the air vents or supply registers.
  • Beyond that, you can also head over to the equipment and see if it's turned on. 
  • Usually, there are indicator lights and you might hear the fans or furnace. 

If the HVAC equipment is powered down, see if the furnace or A/C has mains electricity coming in. 

Check for any breakers, and fuses, and also see if the electrical outlets and safety switches for the equipment are turned off. 

If so, try resetting them and see if the heating or cooling equipment kicks in. 

Step 4: Replace or Recharge the Batteries

After you make sure the issue isn't within the app or your Wi-Fi network, make sure to kick off the troubleshooting process with a fresh set of batteries. 

Why do you ask? Mainly because this helps eliminate most power-related issues, which can affect your cooling. 

If you have the latest Nest Thermostat, pull the display off the wall mount and put in a fresh set of Alkaline AAAs. 

For Nest thermostat E and learning models, pull it off the display and recharge via the Micro or Mini-USB connector at the back. 

With a fresh set of batteries, try adjusting the temperature again and see if the issue resolves itself.

Step 5: Restart The Thermostat

After checking the heating equipment, try restarting the thermostat. A quick restart might help clear out any glitches and get the device to regain full control of the heating system.  

To restart the thermostat via the thermostat's menu:

  1. Open the quick view menu and head over to “Settings”
  2. Then, head over to “Reset”
  3. Pick the option to “Restart”
  4. Provide any confirmations and wait a couple of minutes or so until the device reboots.

To force-restart the device manually:

  1. Press and hold the ring button for about 10 seconds.
  2. After that, let go and press the ring button again. Don't hold it this time.
  3. Then see if the thermostat screen lights up, indicating that the device is restarting. 

After the thermostat has restarted, try adjusting the temperature and system mode to “Heat” or “Cool.”

Step 6: Turn Off Automated Features In Your Nest Thermostat

Sometimes, the schedules or home/away assist features on your thermostat might be interfering with the manual settings. In that case, you can try disabling these features and try again. 

The settings you might have to change are:

  • Disabling Auto-Scheduling Function
  • Turning off Home/Away Assist
  • Configuring Eco Temperatures to “Off”
  • Clearing your thermostat's schedule. 

To learn more about disabling these settings, don't forget to check out this article. 

Step 7: Update Thermostat’s Firmware

Beyond turning off the automated features, it's also a good idea to check for any pending updates. An update can usually help fix any bugs and get your thermostat back in working condition.

Usually, Nest devices update themselves automatically, but in any case, you can also confirm an update via the settings menu.

Update Firmware on the Nest Thermostat (2020 model) 

  1. Wake up the thermostat home screen and head over to the Quick-View menu (by pressing into the thermostat)
  2. From the Quick-View menu, navigate to “Settings” 
  3. Go to Version Update
  4. The thermostat will display the current firmware version along with an option to update.

Update Firmware on the Nest Thermostat E and Learning Models

  1. From the Quick-View menu on your thermostat, select “Settings”. 
  2. After that, scroll to “Software Update.”
  3. You will be greeted with a menu indicating the current version along with the option to update.

Beyond this step, you might have to troubleshoot electrical switches and even fiddle around with the thermostat wires. So if you're not comfortable diagnosing electrical components, I highly recommend getting help from a certified professional. 

Step 8: Verify Compatibility With The HVAC System

Before digging into the breakers or thermostat wiring, it's a good idea to confirm that your Nest thermostat is indeed compatible with your existing HVAC system. 

Usually, Nest thermostats are compatible with most low-voltage (24V) systems, but there can be some exceptions, especially when you have a proprietary system. 

So if you're setting up the Nest thermostat for the first time, make sure to check compatibility. Beyond that, you can check the wiring and equipment configuration on your Nest thermostat. 

If anything doesn't match up with your existing HVAC equipment, you will have to reconfigure it as necessary. 

Step 9: Check the Wiring

Your Nest thermostat actually cannot know for certain if your HVAC equipment turns on. It simply provides the commands and doesn't get any feedback from the system. 

So in most situations, the thermostat might be functioning as usual but the signal might not be getting into your AC or furnace. Therefore, it's important that you check the wiring for any errors. 

When it comes to the wiring, you need to check it at two locations:

  • The Sensed Equipment on Your Nest thermostat's settings
  • The actual physical wiring behind the thermostat display

Check the “Sensed Equipment” Via the Thermostat Settings

You can access the sensed equipment via mobile apps or the thermostat itself. However, I recommend carrying this out via the thermostat display, especially if you're running into connectivity errors. 

Check Equipment Via the Google Home App

  1. Open the Google Home app on your smart device
  2. Select your home (if you have multiple set up)
  3. After that, find your thermostat. Usually, it’s on the “Favorites” or the “Devices” Tab. 
  4. Select your thermostat and then head over to “Settings”
  5. Then, scroll down to “Device information.” 
  6. After that, head over to “Equipment.” The app will show you the current wiring setup along with options to check the equipment type as well.

Check Equipment and Wiring Through The Google Nest App

  1. Open the Nest app
  2. Select your thermostat
  3. Head over to “Settings” on the thermostat’s home screen
  4. Navigate to “Technical Info” and select the option labeled “Equipment”

Check Wiring and Equipment Information Via the Thermostat Display

  1. Press the thermostat ring to bring up the Quick-View menu. 
  2. After that, turn the ring to Settings and press to select it. 
  3. Turn the ring all the way to Technical Info and enter that menu. 
  4. After that, select the “Equipment” Menu. 

Here, the thermostat will pull up a representation of the thermostat’s wiring and show you which wires are detected and which ones are unconfigured or undetected. 

The wires represented in blue are detected and the ones that are orange or grayed out are unconfigured or undetected. 

If you don't understand what any of the wiring means, don't worry. Simply snap a photo of this menu and start checking the actual wiring on your thermostat.

Check the Physical Wiring on Your Thermostat

After you note down the detected wires on your Nest thermostat's settings menu, you must see if this wiring setup matches up with the actual wiring configuration behind your wall.

To do so, simply remove the thermostat from the wall mount. After that, check the wiring in the thermostat's terminals and cross-check them with the configuration that was shown in the settings menu. 

More often than not, they should match. However, if a wire is missing or undetected, you might have to troubleshoot the wiring.

Troubleshoot the Wiring

If a wire shows up as “undetected” in the equipment sense menu but there is one installed physically, the connection might be loose or damaged. 

Try pulling out the wire in question and checking for any signs of damage. Make sure the wire is properly stripped and reinstall the wire. Also, don't forget that the connector on the terminals must be held down to make a firm connection. 

Check for any other inconsistencies and try re-installing the thermostat and seeing if the menu picks up on the missing wire(s).

Step 10: Troubleshoot the C-Wire

For the majority of systems, a C-wire, connected to the Nest thermostat is highly recommended since it resolves any power issues and helps the thermostat run a lot more efficiently. 

So if you don't have one installed already, now might be a good time to consider setting one up. To learn more about C-wire and possible alternatives, check out this article. 

If your thermostat already has a C-wire installed, try removing it and checking if the heating or cooling turns on. In some systems with cool-only or heat-only modes, taking out the C-wire can actually help. 

Step 11: Bypass the Thermostat

If you don't mind tackling a little electrical DIY, you can try to bypass the Nest thermostat by replacing it with your old thermostat. 

However, if you don't have an old thermostat, you can try shorting the wires between the Rh and W (for heating) or Y (for cooling) wires. Here's how:

  1. First, turn off the power to the thermostat
  2. After that, pull the thermostat display off the wall mount
  3. Remove the Rh and either the W (for heating) or Y (for cooling) wires from the Nest thermostat's terminals
  4. If you have wire nuts/splice connectors, you can try to jump the Rh and W wires. Otherwise, you can simply twist them together. However, make sure they don't break.
  5. After making sure this jumper connection is secure, turn on the power to the thermostat.
  6. See if the heating/cooling equipment turns on. 

Here, if either piece of equipment turns on, it implies the issue is within your thermostat and that your HVAC equipment is fine, for the most part. 

On the flip side, if the heating equipment doesn't turn on, your HVAC system might be malfunctioning. In whatever case, I recommend getting help from a professional. 

Step 12: Troubleshoot or Perform Maintenance on Your HVAC System

If the HVAC equipment didn't turn on, even after following the previous steps, these devices might be in dire need of maintenance or repairs. 

You might have to perform maintenance on the system or get help from an HVAC technician to figure out what's wrong. 

Usually, when the heating or cooling equipment doesn't turn on, it can be due to: 

  • Tripped safety switch or disconnect
  • Clogged condensate drain pump
  • Clogged filters
  • Blocked vents
  • Faulty control board
  • Dead blower fan
  • Stuck reversing valve (if you have a heat pump system)
  • Refrigerant leak
  • Broken flame sensors
  • And a lot more.

For the average consumer, fixing these issues by themselves is simply not doable. That's why I recommend getting help from a professional as soon as you identify the issue to be within the HVAC equipment and not the thermostat.

Step 13: (For Heat Pump Systems): Switch the O/B Wire Setting

If you have a compatible heat pump system, you can check for and toggle the reversing valve configuration, termed the O/B Wire Setting.

Toggle the O/B Wire Setting In Your Nest Thermostat E and Learning Models

  1. Wake up the thermostat and navigate to the settings
  2. Go to “Equipment”
  3. After that, the thermostat will display the wiring representation. Here, select “Continue”
  4. Then, the system will ask you to configure the type of HVAC devices you have. Select “Heat Pump”
  5. Toggle to the option that’s not the default. So if “O” is highlighted, select “B” or vice versa.
  6. Confirm your changes, return to the home screen, and see if the issue resolves itself.

Switch the O/B Wires In the Nest Thermostat (2020 Model)

  1. Open the Google Home app on your smart device
  2. Then, select your home and pick your thermostat
  3. After that, tap on “Settings” located at the top right
  4. Then, tap on “Thermostat” to access your wiring and equipment information
  5. Scroll to “Heat Pump”
  6. Then flip the O/B wire setting
  7. Test the system and see if your heating or cooling comes back to life and is in the appropriate system mode. 

Step 14: Factory Reset the Thermostat

Before calling in the cavalry, there's one last thing you can do: factory reset the thermostat. 

 A factory reset might help clear out the issue since the thermostat has a chance to start fresh and you can reconfigure its wiring and installation settings. 

However, only carry this out as a last resort since a factory reset will delete your schedule and custom settings.

Final Step: Call in the Professionals

Diagnosing the HVAC equipment for fixing a faulty thermostat is just not possible by yourself. Therefore, I recommend getting help from a professional if you've exhausted all the steps mentioned above. 

Conclusion

A Nest Thermostat that's not cooling can be a result of many factors.

More often than not, it could be due to incorrect settings, a faulty HVAC system, or a malfunctioning thermostat.

So make sure you follow the steps laid above and, if possible, get a professional to take a look at your HVAC system and thermostat. 

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