I decided to report two problems that have been outstanding for a while (only minor problems to me).
1. The interactive on my main box did not work (M044 error)
2. I didn't know the pin code to use interactive on my other boxes.
So, at 9:15am I ring 150, listen to the options and choose CS. The call was answered in 3 minutes. For the fault they advised me to ring 'faults' on 151(fair enough). For the pin code they told me what the default was, and to try that. If it failed, ring back and they would try and reset it (it was my choice not to try it there and then, if you are wondering).
Okay, phase 1 complete, it's now 9:25 and I ring 151 (which seems to be the same as 150 ..) and choose faults. This time my wait is a little longer - it takes 10 minutes to get through. I explain the problem and that i have rebooted the box (twice) so the guy moves on to testing the box. He gives me the commands to bring up the status, and when we reach the correct page - the status is 3. He immediately says I need an engineer for this. okay I say, expecting it to be tomorrow at least - but no, I am booked for 12pm to 6pm this afternoon. I ask for a call from him before he arrives.
So, then I wait - and sure enough at 1:30pm (ish) I get a call from the engineer saying he will be about 5 mins, and sure enough he turns up about 5 mins later. A few quick tests and he pronouces my box as duff (no return path). Off to the van and back with a new box. All fitted 10 mins later.
So from report, to brand new box - four and a bit hours. WELL DONE ntl is my view.
(oh, and the default pin failed, so I will have to sort that when I get back home from London).