Hello there were you previously receiving Ch20?
Thank you for your reply
Were you previously receiving this channel?
Is there another TV in your home that is connected to the same aerial and receiving this channel?
Does your neighbour receive this channel?
What transmitter is your aerial pointed at please?
Here is a link to your manual
On page 18/32 it shows how to do an "Auto Search" of the channels in your area.
Please kindly try retuning your TV and tell me if you can now see the channels?