Signal is probably listed somewhere near where you found the SNR, on »
192.168.100.1 (although I don't know for sure about that modem, no personal experience). An amp is a signal booster, usually a small box that has an input and an output, as well as a power adapter. It just boosts the signal from the cable line throughout your house, although most consumer amps don't actually do anything with upstream signal, except degrade the signal more. If the signal is bad coming in though, you're just amplifying a bad signal... which doesn't help. I guess the heater could be causing some inference? I doubt to the point that it'd cause T3/T4 timeouts but I don't want to say "not possible" because I really don't know the extent of what a heater could do to a coax line. Try and find your signal levels. Those SNR's look good as long as they're staying there. See if they fluctuate over a few day span, along with the signal levels if you can find them. If your signal is changing by 3dbmv or more... that's usually a problem.