Our new Samsung HDTV has a built in digital receiver and is picking up most Freeview terrestrial channels each time we do a scan, minus One, 2, TVNZ 6 & 7. 
The reception is fine on the channels we pick up with no pixelation. 
Any ideas why we can't get the above channels?

I'm not sure which Wellington transmitter the UHF aerial is aimed at but we're located in the CBD and this is an apartment building, so no access to the aerial. We are getting One and 2 fine on analogue.