A method to continuously monitor for tube leakage in a shell and tube thermosiphon reboiler for heating feedstock in a fractionating column includes: determining the column is in service by continuously monitoring an input flow of the feedstock into the column; determining the reboiler is inactive by continuously monitoring an output valve of tube-side heating fluid from the reboiler; determining the reboiler is losing the heating fluid by continuously monitoring an output flow of the heating fluid from the reboiler; determining the reboiler is heat exchanging by continuously monitoring a temperature difference between input and output flows of shell-side bottoms fluid with the column; and determining the tube leakage in the reboiler is taking place when the column is determined to be in service, the reboiler is determined to be inactive, the reboiler is determined to be losing the heating fluid, and the reboiler is determined to be heat exchanging.