Thermostat displays E42 and cannot connect to Wi-Fi

Note: This is a network configuration issue, not a high-voltage electrical fault.

• Reboot network equipment: Power cycle your modem and router by unplugging them for 30 seconds and plugging them back in. Wait until Wi-Fi is fully restored.
• Check router DHCP settings: Log into your router and ensure DHCP is enabled and there are available IP addresses in the pool.
• Move router or add extender: If the thermostat is far from the router, relocate the router closer or add a Wi-Fi extender to improve signal strength.
• Reconnect thermostat to Wi-Fi: On the Honeywell Home thermostat, go to Wi-Fi settings, forget the current network, and reconnect by entering the correct SSID and password. Use 2.4 GHz if dual-band is available.
• Update firmware via app: Open the Honeywell Home / Resideo app and check for thermostat firmware updates. Apply any available updates and retry the connection.
• Advanced: If your router uses unusual security (WPA3-only, hidden SSID, MAC filtering), temporarily simplify settings to WPA2-PSK and visible SSID to test connectivity.