How to reset FortiGate Firewall when you forget the admin credentials?

In a scenario where a FortiGate Engineer is asked to factory reset a Firewall for which no one knows the admin credentials, let's assume that there is no reset button available on the box. This article will help to tackle the situation. This will only apply to FortiOS version before 7.2.4. Starting from FortiOS 7.2.4 the maintainer account is removed and this method to reset the admin password will no longer work. Follow the below steps. 

1. 
Power reset the Forti box.

2. 
Login as maintainer 

3. 
The password should be given in the below format
bcpb<Serial number of the particular fortigate firewall>
For example if the serial number is FGT12DFHG344 then password should be given as bcpbFGT12DFHG344. 

Note: Once the user enters the username then the password should be entered within 10 seconds. Otherwise the box will only restart.

4. 

Once you log into the box then provide the below command to factory reset the firewall. A warning will appear. Press y and hit enter. The Firewall will reboot and load the basic configuration.

#execute factoryreset

This operation will reset the system to factory default!

Do you want to continue? (y/n)