Every 3 of 4 times I turn on my tv it will say “no signal”- even when there are no outages in area. I either have to reset power cable or reset from phone app. I have played with cables, they sent a new box, then a new modem. Nothing has been fixed and I am tired of the run around each time I call or chat. It has been countless hours with no solution. Anyone else have any luck? Their statement around committing to respect customers time, simplifying experience, and making things right has been far from the truth. I have screen shots of promises to call back and to adjust bill- none of it happened. A week went by after a modem was supposed to be delivered- oh, I dont see that, it never went through. Fed up.
do a test next time it happens. just unplug the HDMI connector from the back of the set top box for 10-20 seconds and plug back in to the very same HDMI port (might want to turn it around to be sure you connect it correctly). does video come on? another way is to use the TV's remote and change HDMI input source to something else (like a DVD player then back to the set top box. worked too?
One possible fix is to swap the HDMI cable for a new one. And maybe try swapping in replacements for the failing devices one at a time - both the settop box and the TV itself if possible. Maybe you can connect to a different HDTV or an computer monitor even if it does not have speakers - seeing the successful HD video should be sufficient for any test.
You mentioned modem , but a modem is not necessary for watching Cable HDTV. The most reliable way to watch cable HD TV is via a tuner that does not require an internet connection, such as an HD-DTA.
A device such as HD-DTA will provide perfect TV picture in cases where the signal is way too degraded for an internet modem. Not sure degraded-signal-from-coax is the case for you... But... HD-DTA are provided at low rental cost or free of charge from xfinity if you select the proper tier/plan, such as limited-basic + Internet double play.