I used to have problems with not getting certain channels, a little bit of research revealed there was a problem with the digibox power supply. It's supposed to be fairly common with the Grundig box.
I bought the kit available and replaced most of the capacitors, it's okay now.
The picture's gone off 3 times tonight, normally it's just every few days.
The picture doesn't freeze, you just get the same blue screen that you would get if you switched onto a channel that you hadn't payed for.
The output from the box goes into the video and then into the TV via scart and coaxial.
I assumed I didn't have a warranty because after the first 12 months I extended the guarantee but haven't bothered for the last 3 years.
I'll have to give Sky a ring!