Hi Matteo,
We do allow removal of the cooler. However, there are a couple conditions to still be covered under warranty:
1. The card must be returned in it's original state (no damage to either the card or the cooler, stock cooler must be on)
2. Failure of the card must not be caused by the removal of the stock cooler or the installation of an aftermarket cooler. ie - if you put a water block on and it leaked, that would void the warranty
Please let me know if you have any further questions, or feel free to contact our support team directly at 1-877-596-6822 9:00am – 6:00pm PST Mon – Fri or send an email to support.us@zotac.com
Sincerely,
ZOTAC