I recently had to back up a site and found that the documentation supplied for doing this did not fully meet my requirements, especially when it came to the step where it asks for the PostgreSQL superuser password.
To overcome this I did the following:
In C:\Program Files\Qlik\Sense\Repository\PostgreSQL\9.3\share\ I made sure that there was a file named pg_hba.conf with a at least the following fields:
# TYPE DATABASE USER ADDRESS METHOD
local all all trust
Then you should create a file in C:\Program Files\Qlik\Sense\Repository\PostgreSQL\9.3\bin\ called pgpass.conf with the following contents: