E73 error message and power and wiring are all on

[DPP1]

• Error message 
• E73
• Power is on
• Wires are connected

[kcruzgonzalez · Accepted solution]

Hi @DPP1,

Thank you for posting in the community. I'm sorry to hear you're encountering an E73 error message with your Google Nest device, even though the power and wiring appear to be all set. I understand how concerning it can be to see an error like this, and I'm here to help you figure out what's going on.

The E73 error message on a Nest Thermostat usually points to an issue with the power being supplied to the thermostat or a problem with the wiring itself, specifically related to the C wire (common wire) or insufficient power from your heating and cooling system.

Even though you've confirmed the power is on and wires are connected, let's go through some troubleshooting steps that often resolve this specific error.

Here's what we can try:

1. Check the C Wire Connection:

   • The C wire is crucial for providing continuous power to your Nest Thermostat. A loose or improperly connected C wire is a common cause for the E73 error.

   • Safely remove your Nest Thermostat display from its base.

   • Carefully check the C terminal on the backplate to ensure the wire is securely inserted and making good contact. Gently pull on it to confirm it's not loose.

   • Also, check the other end of the C wire connection at your furnace or air handler. Make sure it's firmly connected there as well.

2. Verify power at the system control board:

   • If you're comfortable, you can check the wiring directly at your heating and cooling system's control board. Ensure all wires, especially the C wire, are properly seated in their respective terminals.

   • Important Safety Note: Always turn off the power to your heating and cooling system at the breaker box before touching any wiring at the control board.

3. Check for Blown Fuse in HVAC System:

   • Sometimes, a low-voltage fuse (often a 3-amp or 5-amp car-type fuse) on your HVAC control board can blow, leading to power issues and an E73 error.

   • Again, make sure the power to your HVAC system is off at the breaker before checking or replacing any fuse.

   • If you find a blown fuse, replacing it might resolve the issue. If it blows again, there might be a deeper electrical problem with your HVAC system that needs professional attention.

4. Nest Power Connector (if applicable):

   • If you're using a Nest Power Connector because you don't have a C wire, please double-check its installation. An incorrect connection of the power connector can also lead to power-related errors.

   • Ensure the power connector is wired correctly at both the thermostat and the HVAC system.

5. Restart Your Nest Thermostat:

   • Sometimes a simple restart can clear temporary glitches.

   • You can do this by taking the display off the base, waiting a few seconds, and then snapping it back on.

6. Confirm Compatibility:

   • While less common for an E73, it's always good to ensure your specific HVAC system is fully compatible with your Nest Thermostat. You can use the Nest Compatibility Checker online.

After trying these steps, please let me know if the E73 error persists. If it does, any additional details you can provide about your HVAC system (e.g., conventional, heat pump, what wires are connected besides the E73 wire, could you tell me which specific Nest Thermostat model you have?) would be very helpful for further troubleshooting.

Regards

Kevin