My Archer C1200 is not showing 2.4Ghz. It only shows 5ghz. When i try to reboot the router it shows for some time and again 2.4ghz is disappearing.

I have restored the factory default settings too, but still 2.4ghz is not coming now. So what might be the reason? I purchased this router last year in May. It hasa 3 years warranty. will  they replace new router? or will they repair router?