I searched the AskUbuntu and got to two questions about the same issue, which I could not answer because I don't have enough karma :(. So I am posting the solution here.
After clean install, and installing the printer hplip, also install HPLIP Toolbox from the software centre.
Now, if you use 'Simple Scan' from the dash to scan a document, the HPToolbox will prompt you to install the required plugin. You can also install the plugin directly from the HPToolbox on the actions tab.
After this, my scanner works perfectly.
(Scan via network to pc).