Abstract: The current at a deflection electrode 23, 25 of an electrostatic deflection continuous inkjet printer 127 is monitored. If the current reaches a level higher than normal for a clean print head but below the current required to trigger an automatic shutdown, a warning is generated. The warning indicates that an automatic shutdown is likely to follow unless the print head is cleaned. This allows the operator to shut the printer down in a planned manner for cleaning. The warning may be provided at the printer 127 or it may be provided by an external system 121, 129 which allows personnel who are not at the printer to be alerted. The monitoring may be done by the printer or information about the deflection electrode current may be provided to an external system 121, 129 that performs the monitoring.