An inkjet printing system which provides feedback to enable the user to determine whether various replaceable components such as print cartridges, valve holders, and service station cassettes have been installed in proper position. The system includes a printhead carriage and a first sensor feedback device to determine whether a printhead is installed in an operable position on the carriage. The system also includes at least one off-carriage ink supply to which a printhead or printheads on the carriage is/are periodically connected for periodically providing ink to the printheads and a second sensor feedback device to determine whether the replaceable. off-carriage ink supplies are installed in an operable position. At least one replaceable printhead servicing module is also provided positioned to engage one or more printheads when it is moved into a printhead servicing station and a third sensor feedback device which includes a sensor on the carriage is used to read indicia on the servicing module to confirm that the servicing module is installed in an operable position in said servicing station. Separate safety doors provide access to the printhead or printheads, off-carriage ink supply or supplies and servicing module or modules.