After troubleshooting. you discover the following:

The column was running smoothly but not well. Reflux rate was too low, so it precluded significant fractionation. The column pressure was $100$KPa below design. Whenever the pressure reached $130$KPa, the reboller pressure exceeded the hot$-$oil pressure. The relatively low$-$boiling toluene then flowed into the hot oil and flashed. This generated a large volume of vapor that then backed hot oil out of the reboiler. The toluene vapors passed on into the main fractionator and flooded this tower. Only a small amount of vapor, but no liquid, was being produced from the reflux drum, which should have produced mainly liquid.

Explain three possible cause for the errors you observed.