That would suggest to me that there is an issue with the recorder passing the live tv signal on to the tv. Perhaps get a workshop to investigate/service tthe recorder ?
The only other thing I can think of is the recorder may have a more sensitive receiver than the tv and is able to pick up the signal when the tv can't. But I think this less likely. I'd have hoped the recorder would boost the signal.
What you might try is to plug the aerial directly into the tv, leaving out the recorder, and see if the tv can find the signal then.