Sometimes people experience problems with the ITV/C4 multiplex (and also the one that carries five) because of the different transmission mode that allows more channels to be carried, but reduces the effective signal strength.
This can sometimes cause problems when the weather changes (due to the inversion effect).
If you rescan for channels on your box and don't get the ITV/C4 services restored, then you may need to get a new Class I aerial to get reception all the time. However, you should check your cables and connections are in good order first.
John Rowson: If your getting 'no signal', then the TV/box is telling you just that. BBC channels might be OK (although since we have no idea where you live or what transmitter your using, we cannot really say), but it sounds like you have a problem with your aerial system - most likely a damaged cable, etc. If BBC signals are strongest, than they might still just about work, whereas the rest have gone kaput. If its the trasnsmitter, you can ask people nearby, and can check the state of the transmitter by looking on this site.
Dont retune - if everything was fine before, it will essentially 'untune' your set, which makes things worse. Instead, check signal strength on all muxes - if the BBC ones are just holding on, then its an aerial system problem. Follow the signal path back from the TV. It could be as simple as a lose or duff aerial lead - which are cheap to swap out. If that doesn't work, follow it up. If its on the roof, then most likely you'll need a professional to look.
Deene White: Hi, Deene. To get help from this website, we need to know roughly where you are so that we can look into transmitter faults for you. Please come back with the postcode of a local shop, Garage or Post Office. You also need to check whether your neighbours are having exactly the same problems as you, because if they aren't. then there may be problems with your installation that you might need to go through, so ask your neighbours and then report back to this site with a postcode or town name. Richard, Norwich.
Ryan Leask: Hi, Ryan. Are you sure that your Mum & Dad get their tv from a satellitedish rather than terrestrially from a tv aerial on their home? Richard, Norwich. PS If they use a conventional aerial, they should be using the Weisdalerelay ( Freeview Light) transmitter which is part of the Bressay transmitter group!
Ryan Leask: In addition to that said by Richard Cooper. Should your parents indeed be using a Freesat box? then the problem referred to can be caused by a number of different reasons, these ranging from either the satellitedish having been moved (possibly blown) out of alignment, or a fault having developed on the LNB fitted on same, or even failure of the actual Freesat box itself.
However, more information is required in order to assess which of the aforementioned is most likely to apply, such as the model number of the Freesat box in question, and have your parents carried out a signal check on the box? this usually accessed via the set up menu.