A Roku cannot turn your tv off. It does not have that ability. Only the remote can turn off your TV. Have you tried plugging it into your TV? Not the receiver?
Settings > Home screen > Shortcuts > TV Off
Enable that option.
Now [HOME] [Right arrow] [Up arrow]
Select TV Off. Press OK.
DBDukes
Roku Community Streaming Expert
Note: I am not a Roku employee.
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But you are doing that. You have to actually click on it. He’s saying it’s happening all on its own. I am aware of the off channel button on the Home Screen. But he isn’t talking about that
I get that. But Roku does have the capability to turn off a TV. It may not be the Roku device doing it. Or it may be. The Premiere may be getting a stray IR signal from surroundings. Remember, the Off that's added to the menu is an app in the sense that there is a shortcut code for it. Depending on which Premiere and which remote, if there's a problem, it could be turning it off. I realize it's not likely, but that's not impossible.
I don't think this is what's happening, by the way. But not because the Roku can't. It can. But, like you, I think it isn't doing that. Something else is wrong.
DBDukes
Roku Community Streaming Expert
Note: I am not a Roku employee.
If this post solves your problem please help others find this answer and click "Accept as Solution."