It could be, I hear they're pretty unrealiable even though I haven't had problems. It could be a faulty dimmer also.
I'd unplug that sucker since 105 is hotter than what I would be comfortable with and replug it into a different outlet. Set the dimmer and recheck the temps to see if they get any lower.
On the note of measuring temps: are you using a temp gun, a therm with a probe, something else? Are you measuring on top of the substrate surface or directly on the glass (if you have a tank) or he plastic (if you have a tub)?