Try holding the flame slightly further away or turning down the torch a bit, if your combusting you are most likely heating the battery too quickly. I try not to heat any faster than a 30 sec click on the battery, the lowest i would go is around 25 sec.
You can try testing your flame length/technique by installing an empty chamber and time the heat up while aiming for a 30 sec click, set your flame around an inch long maybe and see how quickly that heats up.
What kind of hit you looking for?
This chart should help give you an idea of some heat up times to aim for then you can fine tune it to your liking
If you have a smaller lower powered pocket torch that CANT get the thermal battery to click in 30-35 sec (note: you will not be able to RTL)
Dark roast/Thermal battery = 45-50 sec (great vapour production with great flav)
My Fav
Med roast/Center oven = 35-40 sec (good vapour production with great flav)
light roast/Top ring = 25-30 sec (less vapor production with amazing flav)
If you CAN get the thermal battery to click in 30-35 sec (ie. Blazer firefox ) i would recommend these heating times
Ride the line (RTL)/Thermal battery = 30-35 sec (great vapor production with minimal flav)
Medium roast/Center oven = 20-25 sec (Great vapor production with great flav)
My Fav
light roast/Top ring = 10-20 sec (Good vapour production with amazing flav)