To be fair, if a TV box is regularly restarting, there's very little troubleshooting can be done and it's almost certainly faulty - thus a replacement is an unsurprising result.
Your next move if you have a service fault is to report the fault and get another tech visit out, but having said that.. you can make some basic attempts at identifying the cause of the issue, which sounds like a possible HDD problem.
If live TV is fine (you've hinted at it, but not explicitly said so - is it?), then try pausing this for a short time and watch delayed. Now view that "recorded" programme - is that breaking up? HDD failure if so.
This is exactly it. Live is fine but rewinding even for a second it breaks up. Why does a nee book installed by engineer have a HDD failure
