Nest thermostat displays E1 and cannot connect to the Wi‑Fi network

Safety first: This is a low‑voltage control issue. You normally do not need to power off HVAC equipment, but if you remove the thermostat from the base, switch off power to the furnace/air handler at the service switch or breaker to avoid shorting control wires.

• Check Wi‑Fi signal: Stand near the thermostat with your phone and check Wi‑Fi strength. If the signal is weak or drops, move the router closer, add a mesh node, or a Wi‑Fi extender.
• Verify network credentials: On the Nest, go to Settings > Network, forget the network, then re‑add it carefully entering the correct password. Ensure the router is using WPA2 or WPA3‑Personal, not enterprise authentication.
• Router settings: Disable MAC address filtering or add the Nest thermostat’s MAC address to the allowed list. Ensure the 2.4 GHz band is enabled; some Nest models prefer or require 2.4 GHz.
• Reboot devices: Power‑cycle the router (unplug 30 seconds, plug back in) and restart the Nest thermostat (Settings > Reset > Restart).
• Hardware check: If all networks are visible to other devices but the Nest cannot see or join any network, the internal Wi‑Fi radio on the Nest main board may be faulty. In that case, replacement of the thermostat is typically required.