New freeview tv, all channels but no channel 4?

My Nan got a new tv fitted a month ago. She doesn't watch channel 4 but happened to flick over 2 weeks ago to catch a tv programme and the channel said "no signal". She just switched over but when she went to ch4 again today, same thing. Thing is we have 3 tvs running from the same aerial (with booster) all professionally set-up and the other tv's get ALL channels. When I re-tune tomorrow for the switchover will that cure it or balls it all up? Thanking you all in advance for your help. qsq x