If you are experiencing issues with your Yealink T19PN you can attend to factory reset the unit.
Please note that this will remove all settings from your device.
On your handset, select Menu, then Settings and finally Advanced Settings.
You will be asked for a password. If you purchased the phone from Gradwell, this will be the last six digits of the MAC address, which is shown on the label on the rear of the phone.
If you did not purchase the phone from Gradwell, the default password is admin (n.b. please read this article on the importance of changing the web interface username and password on your device).
Now use the down arrow to scroll to Reset to factory and press Enter.
You will be asked to confirm whether you wish to reset the phone. Click OK to confirm.
The phone will reset and restart.
This will take several minutes - please do not unplug the phone at any point during this process.