Blue Light on Ultra stays on. Black screen on TV when power button on remote is pushed.
Just to clarify since you used "Ultra/TV" a few times. The Power button on the Roku remote does nothing to the Roku device. The power button is a "tv control". It only powers on and off the TV via IR.
You are seeing the black screen because the power button is simply turning the TV on. (not the Ultra). On my Mitsubishi TV, I would see a blue screen if i followed the steps you were doing. Others may see a "No Signal" message screen.
After turning on your TV using the power button (and seeing the black screen), you should be able to press the Home button on your Roku remote. (this will wake the Roku Ultra and you should now be on the Home Screen). Basically the HDMI input is dormant until some action (pressing the Home Button) activates it.
The only time I can use the Power button to return to the Home Screen being visible is if I just turned off the TV and the device has not yet fallen asleep.
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As for the blue light that comes back on, some users have reported that their Ultra (4800 series) light sometimes never goes off. That could definitely be a Roku software/firmware issue, but does not affect everyone's 480x models, so may just be with some TV manufacturers. Just for troubleshooting purposes, see if disabling the TV's HDMI CEC helps with the issue. (use the TV remote, not the Roku remote, to go into the TV's HDMI settings and disable the HDMI CEC. Depending on your manufacturer, the HDMI CEC can be called a few different things.)
I would also try setting the Screensaver Start Time to come on a little earlier (try 10 min), and also use a Roku default screensaver for testing. (ie. don't use a purchased screensaver if currently doing so). Would also try enabling "Auto Power Savings" under your Settings/System/Power/Auto Power Savings and see if that helps keep your light off.
