Dishwashing appliances and methods, as provided herein, may include features or steps such as measuring a first pressure in a sump with a pressure sensor and storing the first pressure in a memory of the dishwashing appliance as a reference pressure. Dishwashing appliances and methods may further include features or steps for measuring a second pressure within the sump with the pressure sensor after measuring the first pressure, and determining that a check valve is failed when the second pressure exceeds the first pressure by at least a predetermined margin.