Thanks everyone for your input - I really appreciate it.
I've got a standard Sky dish with an ordinary twin LNB - I took the Sky Q LNB off. The dish works fine with the Freesat tv I have, and even receives with my old VUduo box - just not with the Octagon.
The twin tuners are both DVB-S2 on the same double module - it's this model: https://www.world-of-satellite.co.uk...2xdvb-s-s2-s2x.
I set the Tuners up (Vix image) with Tuner A Simple 28.2e, and then when that didn't work, tried the same with Tuner B.
The aim is to have the same setup as I did with my Vu+Duo - Tuner A - motorised dish, Tuner B, Freesat. I haven't got the motorised dish mounted yet so I'm just trying to use this time to establish that I have a working box.
I suppose my options are - a) try flashing a different image onto the box such as ATV, or b) send for a replacement.