Z6100 leaks ink in carriage

[Attituc]

Z6100 leaks ink in carriage. I replaced the trailing cables and tubes with a new set (very expensive) and it leaked  once again spilling ink overnight down the side of the machine and the carriage was like a bathtub holding ink. The leak happened with a new set of printheads. Some thoughts:

1) What could have built up pressure overnight?

2) Does the carriage board have anything to do with ink pressure; If so, should it be replaced?

3) Printer prints great but the ink leaks out into the carriage overnight. I'm thinking it is maybe over pressured to leak with new cables and ink hoses.

Help!!! Any thoughts? Thank you

[Valsimot]

What colour is leaked ink? Any specific colour or a mix of colours.

Did you installed genuine HP tubes and trailing? eBay parts from china might be of low quality.

The expiration date on ink cartridges, check those?  The expired cartridge might have higher pressure inside.

[Attituc]

Thank you for the quick response. The ink that leaked both times is the HP 91 Photo black. I replaced all print heads after first leak to be sure. All HP dates are current on print heads. That cost a fortune. I installed genuine HP parts from Partshere in regards to the tubes and trailing set. I replaced all ink cartridges with a set from another z6100ps that was working and it still failed. I took the risk and installed the cartridges  set that was in during the failure into the working one and it did not fail.

Any ideas? I'm exhausted.

[Valsimot]

It leaked overnight that's weird because it's probably not used overnight, if it leaked during printing that would be little less weird. Each printhead has on top air holes for releasing air, and carriage top cover has those pieces that fit holes in the printhead when lowered, check carriage top cover PK part and compare it with other colour.