I tried all the codes listed at xfinity.com/remotes several times with out any luck. I contacted support which was very helpful, excellent service they advised this was a know issue and to try the following.
Push the Setup button until the red light turns green
Enter the code 991
Immediately start pushing on up side of channel change button until the TV turns off, this took about three times on mine.
Push the setup button until the light goes from red to green
Push the TV button, the TV turns on and everything worked.
Sounds odd but it worked, had to try it twice.
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