Cisco VoIP - Basic Troubleshooting for Desk Phones

Basic troubleshooting steps for issues with a Cisco VoIP desk phone. Should be used for issues like being unable to place calls, screen is not functioning, phone is frozen, etc.

Verify Power

  1. Unplug the phone from power, wait 5 seconds and plug it back in.
  2. Check the power source.
    1. Is the power cable plugged into the wall?
    2. Check the connection between the power cable and the power cube, this can become loose. (Note, this is located between the phone and the wall)
    3. Is the power cable plug securely into the back of the phone?

Verify Ethernet Cables

  1. Check the Ethernet connection. Cable configuration should be data jack to phone to computer.
    1. Is the cable plugged securely into the wall jack?
    2. Is the cable plugged securely into the network port (3 box symbol) on the phone? The cable should lead from the wall port directly to the phone.
    3. Is the cable plugged securely into the computer? The cable should lead from the PC port (1 box symbol) on the phone directly to the computer.
    4. Are any of the cable connections loose or poorly fitted? The cable should not be jammed into a jack but it also should not be wiggly. Old cables are a common issue. If you can hold the cable a “certain way” in the jack and the Ethernet reconnects this is an indicator of a bad cable. If this is a problem, please replace the cable.

Verify Handset Cord

    1. Is the handset cord securely plugged into the handset and back of the phone?
    2. Is the handset cord plugged into the handset port? 

Admin Reset (7811, 7841 & 8851)

    1. Press the Settings icon (looks like a gear)
    2. Admin Settings
    3. Reset Settings
    4. All
    5. Reset

Factory Reset (7811, 7841)

    1. Remove the power cord (Or Ethernet cable if powered using PoE)
    2. Wait 5 seconds
    3. Press and hold # while plugging the phone back in. Hold # until the handset light blinks red twice.
    4. Enter the following key sequence: 123456789*0#
    5. The Cisco screen will appear and the phone will be factory reset once network is detected.

Factory Reset (8851)

  1. Remove the power cord (Or Ethernet cable if powered using PoE)
  2. Wait 5 seconds
  3. Press and hold # while plugging the phone back in. Hold # until the handset icon and speaker button icon light up.  The mute button will remain unlit.
  4. Enter the following key sequence: 123456789*0#
  5. The Cisco screen will appear and the phone will be factory reset once network is detected.
    1. The speaker phone icon and mute icon will light up after you submit the sequence to also confirm the procedure was done successfully.

Escalation Info:

  • If none of these fix your problems, please contact the DoIT Help Desk. Please be ready with the following information
    1. The MAC address of the phone Cisco VoIP - How to find a MAC address
    2. The model of the phone.
    3. The room and building where it is located.
    4. The full jack number where it is plugged in.

If you need further help, please contact the DoIT Help Desk for assistance.



Keywordsdoesn't work wont connect cant can't make call calls hard phones 7811 7841 8851 8831 voip factory reset admin settings ethernet cables power unprovisioned verify your network connection network unavailable not working handset   Doc ID78339
OwnerELIZABETH C.GroupVoice Services
Created2017-11-20 17:37:35Updated2023-06-20 10:23:13
SitesDoIT Help Desk, Voice Services
Feedback  8   1