A vertical thermosiphon reboiler has reduced circulation. What are possible causes and solutions?

Causes include: excessive fouling reducing heat transfer (chemical cleaning), vapor lock at reboiler inlet (verify inlet submergence), insufficient static head (check liquid level in column), restriction in piping (inspect for blockages, verify valve positions), excessive pressure drop in return line (reduce two-phase velocity), and flooding at tube inlet (verify proper design vapor fraction). Diagnosis: measure temperatures around circuit, check pressure drops, verify column level. Solutions depend on root cause but may include cleaning, modifying piping, adjusting column level, or changing operating conditions.