As mentioned, the goggles and helmet would not be in the boot heating compartment (at least that isn't the intended location) so the only see the residual heat. I've been using the thermal trekker since the end of November with no issues.
In the owners manual, there is a recommendation to durations to be heating dependent on the setting.
If you put the boots on when they are too warm, though it might feel good, I think (at least for me) it causes your feet to swell a little (heat expands) and my boot buckle need adjusting. Once on the hill and cooler, they need to be adjusted again.
This has only happened when I was cooking them on high on the car ride to the mountain (I have an AC Outlet in the car). I don't run it on high anymore except for maybe at lunch when trying to warm them and in the little time I have, it only makes them less cold.
Part of this is from wearing race boots with no extra room. Any variation changes the fit. I've also been compared to "The Princess and the Pea" when it comes to how things fit and feel, especially boots and shoes. My wife says I'm impossible and on "the spectrum" so consider the source.