jpn005 wrote: ... To change the volume I have to manually change it on the tv. ...
If you still need help please post the brand and model number of your TV set and the kind of remote you have (see http://customer.comcast.com/remotes/ ).
I'm not certain what Comcast equipment & remote you have, but with my Motorola DVRs & the Comcast silver remote, I have found that periodically, I need to press the "cable" button at the top of the remote to get the volume adjustment buttons on the remote to work. Give it a try.