If you switch out remotes and have the Motorola DCT700 box, here is a solution to get your channels to change again.
I switched out my old Comcast remote, the silver DVR3 for the new XR2 remote.
I programmed my TV by using the guide include with new remote, but could not get the channels to change-it stayed on the last channel I was watching before I switched remotes.
Went through Comcast help desk. Nothing worked. Thought it was possibly the DCT 700 box and was going to switch that out.
Finally searched the web and found the solution.
Simply press "Setup", followed by the B key. The light will flash green and you are good to go!
The manual with the remote says nothing about this. I sent an email to Comcast to let them know to add this to the manual and online. Quick fix if it was part of the manual.
I had EXACTLY the same problem, and ended up with exactly the same solution (no thans to Comcast tech. support - they could not hlp with pairing either my TV or the cable box). I still have a single problem though- while I can change volume on TV and change channels on DCT 700 cable box, and am able to turn the TV on/off, I am unable turn the cable box on/off - it has to stay on all the time.
Are you able to use your XR2 to turn the cable box on/off when you press the All Power button? Thanks!