Help getting started with Roku devices, including setup, connecting your device to your TV, linking a Roku device to your account at my.roku.com/link, adding channels, subscribing to services, and more.
My Ultra is connected to an LG Nano85 4K TV without an issue. In fact, I'm using it to watch YouTube right now. I also have a Premiere 3920 connected to a Samsung 4K TV and an Ultra 4640 on another Samsung 4K TV that works just fine. I don't use a 1080 Roku player anymore, as everything I'm using is 4K capable. My Express 4K+ is connected to a 720p TV. No problem with any of them.
There should be no issue connecting any Roku to a 4K TV, regardless of model. Every Roku ever made, with one exception that didn't have an HDMI connection, supports at least 720p, which every 4K TV will display. If the Roku does not display on the TV, try power cycling the Roku and see if the dancing Roku logo on the boot screen appears. If you can't see that, either the Roku or the TV is defective. If you can try the Roku on a different TV, that may help isolate which item is the problem.
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I have the same problem. Roku Ultra not connecting to the LG Smart tv. I was connecting with the Ethernet to bypass the Wi-Fi issues. But the Roku will still not connect well. I took the Roku unit to another house and it works fine to a old Sharp TV.
I have been having somewhat of the same problem. My Roku works on all of my other tvs (smart Samsung, smart Panasonic) It intermittently loads on the LG smart tv. The Roku home screen will flash on the television but then goes blank and no matter how long you wait, the Roku home screen does not return. I find I have to power off and back on the tv several times and eventually I can get it to work. I haven't tried changing the cord but it works on the other tvs so I doubt that the cord is an issue.