I've been working on a new write up for the high heater, and I've been using it a lot to get a better feel for it.
The central hot spot is a symptom of overheating for sure. And as you mentioned the bowl is pretty much spent at that point, not my idea of a good session at all!
Could be a result of two things. Inhale speed too slow, or button kept ON for too long.
Method 1: Use inhale speed alone to control the heat. This requires a very fast inhale speed, and this will increase the likelihood of central hot spotting.
Method 2: Probably the better of the two, use both inhale speed AND feathering the button.
A session with this method might go like this:
First Hit: Button ON..1...2....3....4....(start inhale, slow/med. speed)...5...6...7....8....9...button off...10....button on....11...button off....and so on.
Second Hit: Button ON...1...2...(start inhale, slow/med. speed)...3...4...button off...5....button on....6....button off....7....button on.....and so on.
If you feel like you need more heat, or it doesn't feel like the vapor is flowing as thick as you want, increase the ON time of the button, so you might toggle it off every 3 seconds, instead of every 1 second.
Sometimes I'll ramp up the heat throughout the same hit by first toggling the button on and off every second, and then slowly increasing the time between toggles around the 10-15 second mark... this seems to give a better "feel" for how things are going... and you can adjust on the fly. It's cool because you can start the hit at a lower temp, then ramp up the temp in the same hit. This is usually how I do the last hit of a session.
I'd be interesting to hear others experienced with the high heater as well.
As
@VaporWare mentioned, feathering the button very softly will essentially create tiny arcs at the contact zone because of the button barely making contact, so avoid it if possible. But I wouldn't worry about it, you'll do no damage either way. And if you are creating a bad arc, you'll know immediately by the back plate heating up quickly. This is much less likely with the new button improvements since the first batches.
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I've been thinking that there may be a need for a Medium heater in the line-up, thoughts?