ROM Flashing and warranty issues
Note: The following content has been copied from this forum entry: http://forum.xda-developers.com/showthread.php?t=1894668 and should be revised. The Free Software Foundation Europe tried to answer the question wether a device's warranty ends by flashing the device with a custom ROM image. This should be worked into the article: https://fsfe.org/news/2012/news-20121106-01.en.html
The problem of unlocking bootloader and warranty have been well described here - http://android-revolution-hd.blogspot.com/2013/03/unlocking-bootloader-or-flashing-custom.html
1. Law in each country is different (mostly based on common law (US & UK) and civil law (continental Europe), but "warranty" term means more or less the same everywhere. In simple words, it is a legal contract that is very often a part of legal transactions. Purchase agreement is not a warranty contract itself. Warranty always must be stated on the separate document. If you were not given warranty document, then most probably you were not given warranty at all. Very often different sellers are misunderstanding warranty with consumer law that gives some separate claims for consumers, but it does not gives warranty.
2. So if warranty is kind of legal contract, it is based on freedom of contracting. It means that a party (e.g. guarantor) can write any terms he wants, as long as they are valid with imperative law (lex imperativus).
3. Keep in mind that the same company can have different warranty terms in different countries. So the fact that your friend in the U.S. received brand new device after 3 unsuccessful repairs doesn't mean it is valid for you, a customer leaving in e.g. France.
4. Everyone who wants to know their warranty terms should read their warranty. Don't relay on what you read on the internet or even in this article. I don't know your warranty terms. That is why this article have just a general, educational context.
Now the main part. I'll try to make it as clear as possible.
1. Read your warranty. Do it like 3 or 4 times.
2. Is there directly written that flashing custom operating system voids your warranty? I'm quite sure it's not. Do you believe that installing Ubuntu over machine with Windows 7 sticker voids notebooks warranty as well?
3. My experience is based on reading my warranty terms. In every warranty I saw there was a term about installing any software that comes from 3rd party company. That means it doesn't refer only to custom ROMs. That refers to Angry Birds as well. And Facebook, and Twitter, and SuperUser, and Instagram etc.. So... another question: do you believe that installing Angry Birds voids your warranty? Well... it might have. Keep reading.
4. The most important thing here is the cause and the effect relation. This means that the guarantor can reject your claim to repair broken device only when the fault is a direct effect of installing software that comes from 3rd party company.
Example: you flashed custom ROM on your Android device. All went fine. Later you installed Angry Birds and one of the birds broke your screen. Guarantor can reject your claim to repair broken screen. But not because of custom ROM you flashed, but because of Angry Birds (of course he needs to proof that the fault is a direct cause of one stoned Angry Bird). Sorry for plain stupid example, but I think you see the picture.
Digression: yes, the party that is rejecting your warranty claims needs to proof their affirmations on why they rejected it.
To conclude: if the fault is not a direct cause of installing software that comes from 3rd party company, then your warranty claims are valid. Of course we speak just about the situation that refers to installing software. Once you throw your device from the 10th floor it is obvious you can not say: "There is no direct cause of installing any software that comes from 3rd party company and the fault so you need to repair my device."
5. Now another interesting part - rejecting some warranty claim doesn't mean that warranty is no longer valid at all. Again - it depends on your warranty statements, but based on mine, it works like this: I broke my internal speaker by flashing some sounds boosters. Guarantor proofed it. So I have no warranty now? I still have. But I have no legal claims about the speaker anymore. One week later my CPU fried out for no reason. There was surely no direct cause between CPU and 3rd party software because I haven't installed any CPU controlling/overclocking applications. Based on warranty terms written in my warranty I still have valid warranty for that and guarantor needs to repair my CPU.
This text is just for education purpose. It's not a law itself so you can't base your claims versus some company on this. I may be wrong in many parts - feel free to PM me and I will make corrections. I don't know law in every country so there might be some differences.