How can I force an app to redownload from Mac App Store? I have purchased an app which didn't download successfully. I deleted the installer and tried to install it again from the Mac AppStore but the download button says "Installed".

I also still have the app icon in my Launch Pad with the download progress indicator on it.

I'm aware of the option + click on the "Installed" button and on the Purchases button, but neither works.

How can I reset this download process to enable me to download the app again?
Answering my own question. I enabled the debug menu and then selected Reset Application, restarted the App Store and now the Download button shows up again.

To enable the debug menu, open Terminal and run

defaults write com.apple.appstore ShowDebugMenu -bool true