Freeview HD retuning problems
I tried retuning my Samsung UE32C6510 today (first time after the digital switchover in my area). Initially, only 17 channels showed up. So I decided to retune my TV. Since then, either none of the channels are showing up, or they're coming scrambled. At one stage, only the 4 HD channels showed up. I tried unplugging the TV & antenna cable for 30 secs, & even doing a factory reset (by pressing info, menu, mute, power in sequence with the TV in standby to go to the services menu). No joy so far. 
Any suggestions?
Thanks for the suggestions & the links Chebby! I think my area is covered by Emley Moor transmitter.
I got this message in the link you provided:
EMLEY MOOR transmitter - Over the next week Emley Moor main transmitter: TV (analogue) Liable to interruption, TV (digital) Possible weak signal, Radio (analogue) working normally, Radio (digital) working normally.
I'll wait until end of next week to see if it resolves.
The aerial was installed only in 2009, so I guess it must be DTV optimised (I hope!).
Re-tuned yesterday & got 83 channels! 
I've just got an email from my Dad saying that he's returned his (newish) Samsung TV and has multiple channels - some weak ones. Is there a away of dealing with this automagically? I've not had such problems with my Panasonic.
Thanks
Usually a full blown rescan (due to a problem) involves powering off the TV at the mains, then removing the aerial lead. Power up TV and rescan without aerial lead connected.
When this is finished, power off at the mains again. Plug in the aerial lead, power up TV and rescan again.
What is your transmitter? Have you got a DTV optimised roof aerial?
Pop your postcode in this to check for transmitter problems...
https://faq.external.bbc.co.uk/templates/bbcfaqs/emailstatic/interferencePage
Try this too...
http://www.digitaluk.co.uk/how_do_i_switch/your_aerial/engineering_works#engineering_tbl
...click on the "Planned Engineering Works by Region" tab and see if your transmitter has any work going on or ongoing problems reported.
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