As other stated, I'm pretty sure it is thermostatically regulated, and probably you haven't feel it heating up a lot due the environmental temperature.
I've used it the whole last winter with much pleasure, when taking the car in the morning with 0°C or less, I could remove the gloves after a minute or so and the steering wheel was very confortable, it never became too hot for me, that's another suggestion of it's automatic regulation.
By comparison, during this mornings, the car is around 12-14°, so I use it, but I feel very little heat in comparison to thet winter.
The heathed seat in comparison are much faster and much warmer, I turn them on them at the lowest setting for less than a minute (also in winter) and then shut them off, otherwise I'll start sweating.
My wife in comparison, use the lower setting for an unlimited ammount of time