ink contamination in printhead z3100

[Jaq11]

Hello,

the Z3100 Glossenhancer/ Grey printhead seems to mix the two inks internally while the carriage sits on the service station. That produces a darker leading edge on the print. (See picture below) After Printing some centimeters the grey gradient disappears continously because the mixed ink is sprayed on the paper and new clean ink flows through the two channels of  the printhead.

Changed the printhead already several times. New printheads are working fine but after some days the issue is back.
Service Station is cleaned.

My opinion is, the printhead is soaking up overnight slowly the mixed contaminated ink from the service station because of underpressure in the Printhead-Tube-Cartridge System.

Only workaround is to remove temporarily the printhead after printing.

Any ideas?

Thank you

[Jaq11]

Same problem here:

First-part-of-print-dark-after-downtime 

and here

first-inch-of-print-in-red-comes-out-pink 

and there

dark-leading-edge 

and one more

z3200-wrong-colour 

cheers, Jaq