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E73 nest error – How to fix

Nest thermostats have revolutionized how we control the climate in our homes, offering convenience and energy efficiency. However, like any sophisticated technology, they can encounter issues. One such problem is the E73 error, which indicates a problem with the thermostat’s power supply. This article aims to demystify the E73 Nest error, exploring its causes and offering step-by-step solutions to resolve it, ensuring your home’s comfort is not compromised.

E73 nest error

Reasons behind e73 nest error

Certainly, here are the key reasons behind the E73 Nest error, each highlighted with important elements in bold for emphasis:

  1. Power Outage or Tripped Circuit Breaker: One common cause is a power outage or a tripped circuit breaker. This can interrupt the power supply to the Nest thermostat, leading to the E73 error.
  2. Wiring Issues: Incorrect or loose wiring is a frequent culprit. Specifically, issues with the wiring in the Rc terminal of the Nest thermostat can trigger this error. This includes both improper installation and wires becoming loose over time.
  3. Furnace or HVAC System Malfunctions: The E73 error might also indicate a problem with the HVAC system itself rather than the Nest thermostat. If the system is malfunctioning or not providing power correctly, the thermostat will display the E73 error.
  4. Faulty Nest Thermostat: In rare cases, the issue could be due to a defective Nest thermostat. Internal hardware issues or software glitches within the thermostat can cause it to display the E73 error, even if there are no external power supply or wiring problems.

How to fix e73 nest error?

Fix 1: Resolving Power Outage or Tripped Circuit Breaker Issues

When the E73 Nest error is caused by a power outage or a tripped circuit breaker, it’s essential to approach the issue methodically to ensure safety and effectiveness. The following steps provide a detailed guide to fixing this problem:

  • Check Your Home’s Power Supply: First, ensure that the power outage is not affecting your entire home. If it is, you’ll need to wait for the power to be restored before your Nest thermostat can function again.
  • Locate Your Home’s Circuit Breaker or Fuse Box: This is typically found in basements, garages, or utility rooms. Familiarize yourself with the layout and labels of your circuit breaker or fuse box.
  • Identify the Tripped Circuit Breaker or Blown Fuse: Look for a circuit breaker that has moved to the “off” position or a fuse that appears damaged. The breaker connected to your HVAC system and Nest thermostat is usually labeled.
  • Reset the Circuit Breaker: If a breaker has tripped, flip it back to the “on” position. This should restore power to the Nest thermostat. Be cautious and ensure you’re not touching any wet surfaces while doing this.
  • Replace a Blown Fuse: If a fuse is blown, you’ll need to replace it with a new one that has the same amperage rating. Make sure to turn off the power to the fuse box before replacing a fuse.
  • Check Your Nest Thermostat: After restoring power, check your Nest thermostat. If the E73 error persists, the issue might be more complex, involving wiring or the HVAC system itself.
  • Ensure Continuous Power Supply: To prevent future occurrences, ensure that your home’s electrical system is in good condition. Regularly check your circuit breakers or fuses to ensure they are functioning correctly.
  • Seek Professional Assistance if Necessary: If you’re unsure about dealing with electrical components or if the problem persists, it’s wise to contact a professional electrician. They can safely and effectively resolve issues related to power supply and circuit breakers.

Following these steps should help in resolving the E73 Nest error related to power issues. Remember, dealing with electrical systems requires caution. Safety should always be your top priority.

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Fix 2: Addressing Wiring Issues

The E73 Nest error often stems from problems with the wiring, particularly in the Rc terminal. Here’s how to address this:

  • Turn Off Power to Your Thermostat: This is a critical safety step. Turn off the power to your HVAC system and thermostat at your home’s main circuit breaker to prevent any risk of electric shock.
  • Remove the Nest Thermostat from Its Base: Carefully detach your Nest thermostat from its base. This is usually done by gently pulling the device away from the wall.
  • Inspect the Wiring: Look for any loose or disconnected wires, especially in the Rc terminal. The Rc wire, typically red, is responsible for powering the cooling system and is essential for Nest’s operation.
  • Secure Loose Connections: If you find any loose wires, firmly reattach them to their respective terminals. Ensure that each wire is securely connected and that there’s no exposed wire outside the terminal block.
  • Check for Corrosion or Damage: Inspect the wires and terminals for any signs of corrosion or damage. Corroded or damaged wires might need to be replaced or professionally repaired.
  • Reattach the Nest Thermostat: Once you’ve ensured all wires are properly connected and in good condition, carefully reattach your Nest thermostat to its base.
  • Turn the Power Back On: Restore power to your thermostat and HVAC system at the circuit breaker.
  • Check for Resolution: After completing these steps, check your Nest thermostat. If the E73 error clears, the issue was likely with the wiring.

Fix 3: Resolving HVAC System Issues

Sometimes the problem lies within the HVAC system itself. Here’s what you can do:

  • Examine Your HVAC System: Check your furnace or air conditioning unit for any visible signs of trouble, such as error codes, unusual noises, or failure to start.
  • Reset Your HVAC System: Sometimes, simply resetting your HVAC system can clear up issues that might cause the E73 error. This can be done by turning off the power to the system at the breaker, waiting a few minutes, and then turning it back on.
  • Check the System’s Fuse: Some HVAC systems have a fuse on the control board. If this fuse is blown, it can cause power issues that result in the E73 error. Replace the fuse if necessary.
  • Inspect and Replace Air Filters: Clogged or dirty air filters can cause your HVAC system to work inefficiently or overheat, leading to power issues. Replace any dirty air filters.
  • Look for Obstructions: Ensure that there are no obstructions around your HVAC system, such as furniture blocking air vents, which can cause the system to overheat.
  • Seek Professional HVAC Service: If these steps do not resolve the issue, or if you’re uncomfortable performing them, it’s wise to contact a professional HVAC technician. They can diagnose and repair more complex issues within your HVAC system.

Addressing these potential causes systematically should help resolve the E73 Nest error. However, when in doubt, especially concerning electrical systems or HVAC complexities, always consult with a professional to ensure safety and effectiveness.

Fix 4: Resetting Your Nest Thermostat

Resetting the Nest thermostat can often resolve the E73 error, especially if it’s related to a minor software glitch or a temporary communication issue. Here’s how to perform a reset:

  • Access the Thermostat Menu: On your Nest thermostat, navigate to the main menu. This is typically done by pressing the thermostat ring.
  • Select ‘Settings’: Scroll through the options and select ‘Settings.’ This is where you can access various configurations and reset options for your Nest device.
  • Find the ‘Reset’ Option: Within the settings menu, look for an option that says ‘Reset’ or something similar. Selecting this option will take you to the reset menu.
  • Choose the Type of Reset: Nest thermostats offer different types of resets, including restarting the device, resetting network settings, or resetting to factory defaults. For the E73 error, you might start with a simple restart. If that doesn’t work, consider a more thorough reset, but be aware that this will erase all your settings and history.
  • Follow On-Screen Instructions: The Nest thermostat will guide you through the reset process. Follow the on-screen instructions to complete the reset.
  • Wait for the Thermostat to Restart: After initiating the reset, your Nest device will take a few moments to restart. Ensure you don’t interrupt this process.
  • Reconfigure Your Settings: If you performed a factory reset, you would need to reconfigure your Nest thermostat settings, including Wi-Fi setup and schedule preferences.
  • Check if the Error Resolves: After the reset and reconfiguration, check to see if the E73 error has been resolved.

Fix 5: Firmware Update for Nest Thermostat

Sometimes, an outdated firmware version in your Nest thermostat can lead to various issues, including the E73 error. Ensuring your device is up to date is an important step:

  • Connect to Wi-Fi: Your Nest thermostat needs to be connected to your home Wi-Fi network to receive updates.
  • Check for Updates: In the settings menu of your Nest thermostat, look for an option that says ‘Software Update’ or ‘Update Firmware.’
  • Initiate the Update Process: If an update is available, select the option to initiate the update process. This will typically involve the Nest downloading and installing the latest firmware version.
  • Do Not Interrupt the Update: Once the update process starts, it’s crucial not to interrupt it. This means avoiding power outages and not manually restarting the thermostat during the update.
  • Wait for the Completion: The update process might take some time, during which your Nest thermostat will restart a few times.
  • Verify the Update: After the update process is complete, you can check the software version in the settings to ensure that your Nest is up to date.
  • Recheck for the E73 Error: With the updated firmware, verify if the E73 error has been resolved.

Performing these fixes can often resolve the E73 Nest error. However, if the problem persists after trying these solutions, it might be necessary to consult with a Nest professional or consider replacing the unit if it’s found to be defective.

Fix 6: Checking and Replacing the C-Wire

The absence or malfunction of the C-wire (common wire) in your Nest thermostat setup can lead to the E73 error, particularly in systems requiring constant power for control:

  1. Inspect the C-Wire Connection: Check if your Nest thermostat setup includes a C-wire, which is typically connected to the C terminal. If it’s missing, that might be the source of the problem.
  2. Secure Any Loose Connections: If a C-wire is present, ensure it’s securely connected to both the thermostat and the HVAC system.
  3. Consider Installing a C-Wire: If your system lacks a C-wire, you might need to install one. This can be a complex task, so it’s often best handled by a professional.
  4. Replace a Faulty C-Wire: If the existing C-wire is damaged, replacing it can resolve the issue. Again, due to the complexities of HVAC wiring, professional assistance is recommended for this task.

Fix 7: Inspecting and Clearing HVAC Condensate Drain Line

A blocked condensate drain line in your HVAC system can sometimes trigger the E73 error on your Nest thermostat due to safety switches that cut off power to prevent overflow:

  1. Locate the Condensate Drain Line: This is usually a PVC pipe near your HVAC system, often leading to the outside or a drain.
  2. Check for Blockages: Inspect the line for any blockages like dirt, debris, or algae growth.
  3. Clean the Drain Line: If blockages are found, use a wet-dry vacuum to clear the line, or flush it with a mixture of water and vinegar to break down any clogs.
  4. Monitor for Further Issues: After cleaning, keep an eye on the drain line to ensure it remains clear and that water flows freely.

Fix 8: System Compatibility Check

Sometimes, the E73 error can be due to compatibility issues between your Nest thermostat and your home’s HVAC system:

  1. Review Nest Compatibility: Check Nest’s compatibility with your specific HVAC system. This information can usually be found on the Nest website or through contacting their support.
  2. Consult with a Professional: If you’re unsure about compatibility, consulting with a HVAC professional or a Nest Pro can provide clarity.
  3. Consider System Modification or Replacement: If your system is incompatible, you might need to modify your HVAC system or consider a different thermostat model that’s compatible with your setup.

Each of these fixes addresses a different potential cause of the E73 error in Nest thermostats. It’s important to approach each solution with safety in mind, and when in doubt, always seek assistance from a qualified professional.


The E73 Nest error, while bothersome, is usually solvable with a bit of troubleshooting. By understanding the possible causes and following the outlined steps, you can often resolve the issue yourself. Remember, regular maintenance and being aware of your home’s electrical systems go a long way in preventing such errors. However, don’t hesitate to seek professional help if needed, ensuring your Nest thermostat keeps your home comfortable and energy-efficient.


What does the E73 error on my Nest thermostat mean?

It indicates your Nest isn’t getting power from the Rc wire.

Can a power outage cause the E73 error?

Yes, power outages or tripped circuit breakers can lead to this error.

Is it necessary to have a C-wire for Nest?

While not always necessary, a C-wire can stabilize power supply to the Nest.

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