BG, The charring on the bottom bar of the frames occurs when the JB200 is not pushed far enough into the hive to overcome the weight of the handle and wiring, causing the heater and pan to be lifted up and come into contact with the frames. This can also cause the heater and pan to become tilted sideways and the liquified acid will spill out reducing the effectiveness of the treatment.

Sometimes ladder comb and other debris will prevent full insertion of the unit, so to overcome this problem keep a scraper handy to slide into the hive opening and clear a path for the vaporizer.