It may be possible that the system feeding the property isn't correctly wired. Are you in a small block of flats which is fed by a communal TV/sat system by any chance?
Its common with with some IRS systems, mostly Fracarro ones for one set of switches/feeds only to carry satellite signals and not terrestrial TV. The idea is that the switch with the combined sat and terrestrial signal feeds the side of the plate that covers sat1/TV & DAB/FM and the feed with just the sat signal goes to sat 2.
It could be that the two cables are the wrong way round in the plate or that your plate is being fed off the switch with no terrestrial signal, which isn't un-common as when the blocks are cabled a lot of the cable crews ( specifically working for one company i know) don't bother marking the cables so its inevitable that this problem occurs.
I used to do this as a job before i gave it up for my sanity, and it was a problem that came up quite often when i was covering the service calls. Everytime it was in a block that ran Fracarro systems. Theres nothing wrong with Fracarro stuff, it just depends on who wired it up.
Nano