Sorry Monkeybreath, perhaps I didnt explain clearly enough. Two of the STBs are working fine - they've received the recent update and appear to have improved ever so slightly regarding performance.
Just one STB fails to work and its not connected to any other STB (although my SACM is joined to it via a splitter too!!! Do ntl like to save time by adding splitters??? Perhaps they have shares in the company they buy them off??