If getting a new remote doesn't work.........
Do you have a plasma TV? there was a customer who we had to deal with when I worked for Telewest and it was the residual frequency given off by the plasma screen was causing the PACE box to change channels by itself.. we went through the 1000 1010 2000 & 4000 boxes with no change it was only when we tried the SA4200 that the problem was resolved. We then had to go back and change that for the SA4000 as the SA4200 has a lower volume output.....
I'm not sure if this affects all plasma screens but the one we dealt with was a panasonic 42" Might be worth a try if you can ask the service engineer to put in a SA box
They don't always carry both PACE & SA though so you may not get this resolved on first visit. unfortunately they guys are not given a choice in what equipment they carry.
Hope this helps.