A portable therapeutic fluid delivery device with a flow detector comprising a heating element and two temperature sensors is presented. Upon activation of the heating element, a flow condition of the fluid inside the delivery tube is determined based on a signal provided by the temperature sensors. A temperature gradient within the therapeutic fluid is detected. The determined flow condition can be one of: air bubbles within the delivery tube, occlusion within the delivery tube, or leakage within the delivery tube. The device can have two parts, for example, a reusable part and a disposable part. Upon pairing of these parts, the heating element and the temperature sensors touch the delivery tube.