How to factory reset a Mitel 5310, 5320, 5330, 5340, IP phone.
1. Unplug the Ethernet cable at the back of the phone and ensure it is powered off.
2. Plug the Ethernet cable back in and during boot up, hold down the up arrow key until the display shows “Configure Phone?” and then make the selections shown below.
Configure Phone? * Yes
Network Parameters? # No
Hardware Config? # No
Phone Mode? # No
Tools And Features? * Yes
Erase PIN? # No
Edit 8021X Settings? # No
Edit CDP Settings? # No
Edit LLDP Settings? # No
Task Bar Setup? # No
Ping Test? # No
DHCP Trace? # No
Video Configuration? # No
Port Options? # No
Disable Pkt Filter? # No
Diagnostics? # No
Restore Defaults? * Yes
Confirm? * Yes
Wait for the phone to reboot. And update us once done.