cool...engineer has just been and sorted the problem. Apparantly the signal level was way off - neg 20? Traced the problem down to the splitter in the cellar being installed the wrong way, i.e. the feed end was going up to the broadband with the actual feed going into one of the outputs, had been that way since the original install so i'm suprised it ever worked!
Anyway, all channels came back on straight away so hopefully problem solved
