Seriously, have you verified the temperature? I can't think of anything else that could be wrong. You did say that the packs swelled *somewhat*, right?
At any rate, if there hasn't been a drop in gravity, then nothing is fermenting, yeast or otherwise.
I use one of the digital thermostats, and it is consistent with the other digital thermostat that I have as well as the stick on thermometer that is stuck to the primary fermenter. Otherwise, I'm not sure how to calibrate.....and honestly, the packs really did not swell much if at all(not like I'm used to seeing)