Monitoring of fluid supply

A printer comprising a supply tank, an intermediate tank, a printhead, a printing fluid pump in fluid communication with the supply tank and the intermediate tank, a printing fluid connection between the intermediate tank and the printhead, a printing fluid level sensor at the intermediate tank, and a controller programmed to:

• activate the printing fluid pump to fill the intermediate tank with printing fluid from the supply tank;
• deactivate the printing fluid pump when the printing fluid level sensor detects that a defined first printing fluid level in the intermediate tank has been reached;
• control the printhead to print a diagnostic image;
• reactivate the printing fluid pump to refill the intermediate tank with printing fluid from the supply tank after a defined portion of the diagnostic image has been printed;
• monitor the printing fluid level of the intermediate tank while the printing fluid pump is activated;
• and
• diagnose operation of the printing fluid pump as a function of the printing fluid level of the intermediate tank.

A user interface of a printer, comprising:

• a first entity to allow a user to trigger printing of a diagnostic plot;
• a second entity to prompt a user to provide a printing fluid supply with a minimum amount of printing fluid stored therein;
• a third entity to inform the user about progress of a diagnostic operation including information about at least one of a printing fluid refill progress and information about a printing progress;
• and
• a fourth entity to inform the user about a diagnostic result as a function of the printing fluid refill progress and the printing progress, wherein the diagnostic result includes a diagnosis of an operation of a printing fluid pump as incorrect if a time period of printing fluid refilling progress is above a threshold value.