Sorry to hear that you're having problems with the STB kanagarajanc. I think the model number of our STB was D4010.
I would ring Faults and explain that you had the earlier problem, a technician was dispatched and "fixed" the problem. Tell them that the same problem has happened again. They should automatically change the box this time - although that's up to them (if they believe the problem is fixable).
Out of the three boxes we have, two have had to be replaced twice over the past three years so Im used to ringing Faults.
Good thing is that Faults are now open on a Sunday from 10am (I think) - so you can call them tomorrow!!
Hope this has helped you.
James