pot/column temps

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im having trouble maintaing temp in the column and pot.i use a propane burner.a 16gal sanke and a 57in tall 3in ss tubing column.its packed to 55in with 6mm raschig rings.the condensor is probobly over kill(it comes out cold cold))it has 1/4in booze line with 3/8in water line.i ran the heat slow last time and wen it hit140degs in pot i backd off heat and heard it boiling.backed it way off.temp rose to 190degs. and stayed felt heat rising up column til it hit the top.gauge spiked to appx 175-180.ran good but prooff dropped quickly.at first i started 180 the after appx 4 liters was at 60pr.it was a 5 gal wash that i dumped 2liters of trailes into.the temp in column continualy rose during this time.am i doing somthing wrong.the column rose to 200degs gradully before i killed the flame.should i preheat column?should i heat slower?thanx for any help!