In respiratory therapy, the jet nebulizer is a cornerstone device, responsible for converting liquid medication into a therapeutic aerosol. Its function is based on a simple but critical engineering principle: the Venturi effect, where compressed air creates a low-pressure zone that draws up and atomizes the medication. However, when a unit fails to produce mist, patient treatment is compromised. This guide provides a systematic, engineering-based approach for biomedical professionals to diagnose and resolve the most common causes of this fault, ensuring equipment reliability and patient safety.