A hard factory reset resets all of the parameters of the phone including network and security settings. This is sometimes necessary for troubleshooting or resolving phone issues.
Unplug the Ethernet cable from your Cisco IP phone. Wait 5 seconds. Press and hold #.
Plug the Ethernet cord into your phone. The green headset and speaker buttons will light up. Wait until the green headset button light goes out then comes back on. Immediately after the green headset button light comes back on, release the pound key (#) and enter the following: 123456789*0#. NOTE: The headset light will turn off after you press 1.
The Mute button will light up. If Mute does not light up, repeat step 5 until it does. This may take up to 10 minutes.
The main phone screen will appear. The phone resets.
Press the Settings (gear) button -> Admins Settings -> Reset Settings -> All Settings.
A hard factory reset restores all settings to factory default, including network and security settings.
Unplug the Ethernet cable from the phone. Press and hold the microphone button.
Holding the microphone button, power on the phone by plugging in the Ethernet cable. There are lights on the left, right and back sides of the phone. When they change from green to red, release the microphone button.
Press and hold the microphone button for about 5 seconds then release it. The lights will blink red twice.
Press and hold the microphone button. After about 5 seconds, the links will blink red continuously, indicating that the hard reset is complete.