nest keeps disconnecting from wifi every day, i have to keep re-adding it.

Diagnosis

The Google Nest Learning Thermostat 3rd Generation frequently drops its Wi-Fi connection due to a critical power deficiency known as "power stealing." When the thermostat doesn't receive constant 24V power from the HVAC system (usually because there is no common "C-wire"), it relies on pulsing the heating or cooling wires to charge its internal battery. When the battery voltage drops below a specific threshold (typically around 3.6V), the device disables the power-hungry Wi-Fi chip to prioritize basic thermostat functionality and prevent a total system shutdown. This creates a cycle where the device stays connected while the battery is full, but as soon as the voltage dips, the Wi-Fi radio shuts off. You can confirm this by checking the thermostat's internal status: navigate to Settings > Technical Info > Power. If the "Battery" voltage is consistently below 3.7V or the "Lin" value is fluctuating wildly, the hardware is shutting down the network card to save energy. Additionally, interference from 5GHz bands can cause the 3rd Gen's older 802.11a/b/g/n radio to lose its lease on the IP address, forcing a manual reconnection.

How to Fix It

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

1. Verify Power Levels: On the device, go to Settings > Technical Info > Power. Note the "Voc" and "Vin" readings. If Vin is below 3.6V, you have a power issue.
2. Hard Reboot: Press the thermostat display ring down and hold it for 10 full seconds until the screen goes black and the Google logo appears. This clears the cached network credentials and resets the radio.
3. Network Reset: Go to Settings > Reset > Network. Select "Reset" to wipe all saved SSIDs.
4. Force 2.4GHz Connection: Access your router's admin panel (usually 192.168.1.1 or 192.168.0.1). If you have "Smart Connect" or "Band Steering" enabled, disable it. Create a separate SSID specifically for 2.4GHz (e.g., "HomeWifi_2.4"). Connect the Nest to this specific band, as the 3rd Gen radio is significantly more stable on 2.4GHz than 5GHz.
5. Static IP Assignment: In your router settings, find the MAC address of the Nest (found in Technical Info > Network) and assign it a Static IP address. This prevents the "DHCP Lease" timeout that often causes the Nest to drop the connection every 24 hours.

If That Didn't Work

• Install a Nest Power Connector: If you lack a C-wire, buy the official Google Nest Power Connector (Part #G7P-S3). This is installed at the HVAC control board (not the thermostat) and provides a constant flow of power, stopping the battery drain that kills the Wi-Fi.
• Install a 24V C-Wire Transformer: If you cannot access your furnace board, buy a 24VAC plug-in transformer. Run the two wires to the "C" and "Rh" terminals on the Nest base. This bypasses the "power stealing" mechanism entirely and provides a dedicated power source.
• Relocate the Router or Add a Mesh Node: If your "Network" signal strength in Technical Info is lower than -60 dBm, the signal is too weak. Place a Wi-Fi extender or a Mesh node (like Nest Wifi or Eero) within 15 feet of the thermostat, ensuring there are no metal HVAC ducts between the node and the device.
• Change Wireless Channel: Log into your router and change the 2.4GHz channel from "Auto" to a fixed channel—specifically 1, 6, or 11. This eliminates "channel hopping" which often causes the Nest to lose its connection.

Heads Up

• Avoid "Smart" Plugs on HVAC: Never use a smart plug or timer on the 24V transformer powering your Nest; any interruption in power will cause the device to lose its network settings.
• Battery Depletion: If the thermostat screen shows a blinking red light at the top, the battery is critically low. Do not attempt to fix the Wi-Fi until the device has been charged via a Micro-USB cable on the back of the display for at least 30 minutes.
• Firmware Updates: Always check for updates in Settings > Software. Google frequently releases patches specifically for the 3rd Gen's Wi-Fi stability.
• Avoid Metal Covers: Ensure you haven't installed a decorative metal cover or "trim plate" over the thermostat that could act as a Faraday cage, blocking the internal antenna.