nest keeps disconnecting from wifi, says it's offline in the app every few days

Diagnosis

The intermittent connectivity of the Google Nest Learning Thermostat (4th Gen) is typically caused by "power cycling" of the Wi-Fi chip. When the thermostat doesn't receive consistent 24V power from the HVAC system (specifically via the C-wire), it enters a power-saving mode to protect the battery. During this state, the Wi-Fi radio is the first component to be throttled or shut down to conserve energy, leading to the "Offline" status in the Home app every few days.

Additionally, the 4th Gen model is sensitive to 2.4GHz and 5GHz band steering. If your router uses a single SSID for both bands, the Nest may attempt to hop to the 5GHz band for speed, only to lose the connection because the 5GHz signal cannot penetrate the wall or the metal HVAC backplate as effectively as 2.4GHz. You can confirm this by checking the "Network" section under Technical Info; if the "Signal Strength" fluctuates between "Fair" and "Poor," or if the "Battery Voltage" is consistently below 3.6V, the device is likely dropping the connection to save power.

How to Fix It

To resolve the connectivity drops, you must stabilize the power delivery and optimize the network frequency. Follow these exact steps:

1. Verify C-Wire Connection: Remove the thermostat display from the base. Check if there is a wire connected to the "C" (Common) terminal. If the C-wire is missing and you are relying on "power stealing" from the Rh/Rc wires, the Wi-Fi will continue to drop. Install a Google Nest Power Connector or a physical C-wire to ensure a constant 24VAC supply.
2. Check Signal Metrics: On the device, navigate to Settings > Technical Info > Network. Note the "Signal Strength" and "1-minute/5-minute" average. If the value is above -70dBm, the signal is too weak.
3. Separate Wi-Fi Bands: Access your router's admin panel (usually 192.168.1.1 or 192.168.0.1). Disable "Smart Connect" or "Band Steering." Create two distinct SSIDs: one for 2.4GHz (e.g., "Home_Wifi_2.4") and one for 5GHz.
4. Reconnect to 2.4GHz: On the Nest Thermostat, go to Settings > Network. Select the newly created 2.4GHz SSID and enter your password. The 2.4GHz band has a longer wavelength and is far more stable for the low-bandwidth requirements of a thermostat.
5. Restart the Device: Perform a soft reboot by going to Settings > Reset > Restart to clear the network cache and establish a fresh handshake with the router.

If That Didn't Work

If the connection still drops after stabilizing power and frequency, try these advanced alternatives:

• Assign a Static IP Address: Log into your router and find the MAC address of the Nest Thermostat. Assign a Reserved/Static IP to the device. This prevents the "DHCP Lease" from expiring, which is a common cause for the device showing as offline every 72 hours.
• Change the Wi-Fi Channel: If you live in a crowded area, your 2.4GHz channel may be congested. Change your router's 2.4GHz channel from "Auto" to a fixed channel—specifically 1, 6, or 11—to avoid interference from neighboring networks.
• Disable IPv6: Some users have reported that the Nest 4th Gen struggles with IPv6 handshakes. In your router settings, temporarily disable IPv6 to force the device to communicate solely via IPv4.
• Install a Dedicated Access Point: If the distance between the router and the thermostat exceeds 30 feet or passes through more than two walls, install a Wi-Fi extender or a Mesh node (like Nest Wifi or Google Wifi) within 15 feet of the thermostat.

Heads Up

Keep these critical maintenance tips in mind to prevent future outages:

• Avoid Metal Shielding: Ensure no large metal objects or mirrors are mounted directly between the router and the thermostat, as these create "dead zones" that trigger the offline status.
• Update Firmware Immediately: When the device comes back online, check for software updates. Google frequently releases patches specifically for Wi-Fi stability and radio power management.
• Voltage Warning: If your battery voltage drops below 3.6V, the device will prioritize heating/cooling over Wi-Fi. If you see this, your HVAC transformer may be underpowered; consider upgrading to a 40VA transformer.
• Avoid "Guest" Networks: Do not connect the thermostat to a Guest network with "Client Isolation" enabled, as this prevents the app from communicating with the device even when it is connected to the internet.