Calculations are made of the heat balance of the vacuum column K-101 of the VDM-2 plant of LUKOIL Neftokhim Burgas AD, which made it possible to disclose the reasons for decline in heavy vacuum gas oil yield with increase in plant load and to discard the hypothesis that the reason for this is perforating of the plate from which the gas oil is withdrawn. It is shown that the reflux yield cannot be increased and the heat required for condensation of the heavy vacuum gas oil contained in the residual fuel oil cannot be removed if there is hydraulic resistance in the lower circulating reflux line.