Most budget boxers don't have an RF output and so don't 'tune' to the TV but rather are attached via a SCART lead and then accessed by the AV button on the TV's remote.
Have you read the Installation Instructions?
T
April 2009
Automatic Answer
While you wait for answers, we may have found some information which could help you.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix dtt receivers.