So the issue boils down to the tools not working with something that isn’t Fairphone OS? That makes sense. We will see if they respond with something else on the email.
Not just that, I imagine, people can do all sorts of things to the phone via software and ruin a phone. However if the phone is using the Fairphone OS and is not working then as long as the warranty is still valid Fairphone have obligations to check the phone.
You will need to be able to revert to the original Fairphone OS to be able to claim on warranty in most situations. Of course if it is clear that it is a purely mechanical issue, then the warranty will still apply. However, if the feature affected could possibly have been affected by an alternate OS, and you are unable to revert to FOS then the warranty would be void.
(Boldening of text is mine)
So basically, it’s as I suspected. If you install LineageOS and the audio breaks due to faulty ROM drivers, they won’t help you with that. If you install LineageOS and then the motherboard or screen breaks, they will help you with that.
So basically, if you don’t want to lose warranty, don’t lock the bootloader when a non-Fairphone OS is installed.
Short answer for EU citizen : no unless the manufacturer can prove the software made the defect which is only possible for a limited number of case. Does rooting your phone invalidate its warranty? (In EU) :: Law is Freedom for the long version and that’s a long time it’s like that, Fairphone and other brands can write what they want, EU law it’s EU law so use your local consumer association if you have any trouble and if you are an EU citizen to make them respect the law.