I purchased a typical mid-range laptop in late March this year. It came with Windows preinstalled. As soon as I unpacked the computer I removed Windows and installed Linux. I have been using it without any problems until two weeks ago. The system kept crashing whenever I was upgrading a dozen programs or more at once. I ran various diagnostic commands and concluded that the cooling system was failing.
I visited the nearest offline customer service with my laptop and logs of the troubleshooters I ran. The technician quickly noticed that I was using a non-stock operating system. He claimed that the manufacturer does not guarantee the machine will run properly in any os other than the preinstalled one, and that my warranty had been invalidated by the swapping of the os. I argued that replacing the stock software with a verified alternative does not pose any danger to the underlying hardware and my warranty is still intact because I never tore the laptop open.
Then he said that it is my job to prove that there is a 0% chance Linux harmed the hardware in any way. I found this argument as absurd as his initial one but he didn't back down so I had to return home.
Is the technician correct? Can warranties expire just by installing software even though hardware was left untouched? Or is he just trying to deny the defect in the laptop and deny the free repair I deserve? Is the burden of proof on the seller or the consumer that the warranty is valid/invalid?