I know this is an old post, but I have the same issue. I've searched for hours online and only found similar issues (RCA L32HD31R tv and XR2 remote not linking no matter what codes you try) with no solutions.
I also just spent 20 minutes on the phone with Comcast support. They agree that this TV and remote are incompatible. They did put in a service ticket with Comcast Engineering, so maybe in the future they'll figure it out.
Question, prior to trying to link my Comcast remote to my TV, I could at least change the volume on the Comcast box (its a different volume setting than the tv volume). Now, since I tried linking the tv and comcast remote, I can no longer change the comcast box volume. Anyone know how to revert back so I can at least change the volume on the Comcast box with the Comcast remote?
CAN’T FIND YOUR CODE? If you can’t program your remote using the codes on the back, follow the steps below. 1. Turn on your TV. 2. Press TV on your remote. Then hold Setup until the TV button flashes twice. 3. Enter 9-9-1 and the TV button will flash twice. 4. Press 1 and the TV button will flash twice. 5. Press the Power button, then press CH+ multiple times until the TV turns off. 6. Once the TV turns off, press Setup to lock in the code.