This came with a stack of components. Every unit was recognized by Chemstation. This unit starts up and goes through its homing sequence and ends with a red light (as did all of the components). The manual states that a red light will occur if there is a problem with any of the components, so we do not know which component (or multiple components) may have an issue. We are not that familiar with this model, so we are offering this as is for parts/repair.