I've been struggling with intermittent problems with my NTL broadband for about 5 years.
It seems that when the weather is very hot and sunny, my cable modem power levels go crazy and the lights go out on the CM. Calling customer services means 30mins on hold at least only to be told to turn it all off and on again. I've had dozens of engineers out but they never really do much apart from say 'it's working now' or 'your power levels are all wrong'.
I've been using Ping Plotter to record the speed of pinging
www.ntlworld.com I rarely get better than 10%-20% packet loss on sunny days, often much worse.
Service tends to be fine at night but intermittent during the day. I would move to BT but I have two phone lines, one of which I use to work from home. BT can't guarantee a continous service with me retaining both numbers.
Any suggestions?