1) The box os not connected to your monitor via an HDMI cable. To be honest, I can't think how else it could be attached, so I think we can discountt that one.
2) The box has missed the mux, or even the correct transmitter. Because you put your postcode in (which is extremely useful!) we can see that Haslingden and Winter Hill are almost at the same distance, and almost on the same bearing. But the former starts at Channel 26, and the latter at Channel 50. If you box is like mine, it starts at the low numbers and works upwards - hence hitting Haslingden first. And Haslingden does not transmit Film 4 in HD...
The other thing could be thats its not a HD box (so a make/ model number would help), but I suspect your simply tuned into the wrong transmitter. Try taking out the aerial lead for the first 30% of the scan (David Lindsay's trick) and see if you just get Winter Hill. Its a bit hit and miss, but it should eventually work. Once tuned in, never retune!
David : Due to a lack of capacity on the relatively new COM7 HD transmitterFilm4 (LCN15) is presently transmitted in SD on PSB2, if you wish to view it in HD then you have to select its +1 (Film4+1) service on LCN45 which is broadcast on the PSB3 HD transmitter, as used by such as ITV HD / BBC3 HD etc.
David : Re: your query on Film4 HD. Please disregard that said in my reply made yesterday @ 9.03PM, as further checking has revealed that Film4 HD (whether +1 or not) is not available as yet on the Freeview platform, and even although +1 is being transmitted on an HD transmitter its only being broadcast on SD.
This being the case, there is no real advantage of using Film4's +1 service on (45) over the normal SD transmission on (15), that is unless having a specific reason for wishing to view Film4 on its +1 service.
Apologies if any confusion was caused by this error.