I got an email from someone who is having a problem where one of their HD channels used to work but now they get a ‘No TV Signal’ blue screen. The answer here is:

Typically the reason this happens is that a broadcaster starts broadcasting on some other frequency, and we no longer receive the signal. We use a table that we get from [our metadata provider], that they get from the FCC, to know which channels are broadcast on which frequencies. When broadcasters change frequencies (either because they switch from a test feed to a production, live feed or some other reason), we don’t know unless the FCC knows and updates their database that [our metadata provider] gets data from. We don’t actually do “scanning” the way that a TV, or other TV applications, do.

If this happens to you submit your problem to Electronic Program Guide Issue Submission Form and we’ll work to get our tables updated.