A method includes engaging a well of a cartridge with a flow sensor of an instrument. The cartridge includes: a rotary valve including a rotatable port and a center port; the well in fluid communication with a channel, the channel including a channel port that the rotatable port is to align to in order to receive fluid from the well; and a flowcell including an inlet gasket in fluid communication with the center port. A source of pressurized air is connected to the flow sensor in order to establish a mass flow of air through a flow path. The flow path extends through one of the flow sensor, the channel, the rotary valve, and the flowcell. The mass flow of air through the flow path is measured with the flow sensor. It is determined if there is one of an air leak and an air blockage within the flow path.