A lot of support requests have come in saying that a channel scan with a Hdhomerun Prime device is returning no channels. Channel scan for the Hdhomerun pulls an xml file from the device from this site:
http://<your hdhomerun device ip>/lineup.xml?show=unprotected
So if that has no channels neither will the HomeRunTV app. To fix this go to:
http://<your hdhomerun device ip>/lineup.html
and click the option to "Detect channels". After that completes the app should be able to find the channels.