800 are usually duplicate channels of those assigned to the 100 range.
The weather is playing havoc with signals at the moment so it may be that this is affecting your usual transmitter but not those duplicates.
It's not possible to reasign channels on TalkTalk boxes, these are fixed by Freeview.
You could try a retune, but be aware that if it's weather related you could lose more rather than restore those missing ones.
Try taking the aerial out and retuning first though as this clears the box memory, then retune with the aerial back in the box.
Hope this helps.
From the 29th of March our TalkTalk Community will move to peer-to-peer support and the TalkTalk team will no longer be here to support with queries. Don’t worry we still have plenty of ways to reach out if you need to speak to TalkTalk directly. For more details check out the link here:
How to contact TalkTalk Broadband - Help & Support.
