Headphone jack not working

My headphone jack just stopped working ouit of the blue. No water ingress, not dropped, no recent downloads, software updates or any other reason to stop it working. I have replaced the charging port/headphone assembly with a brand new one. I have reset the phone to factory standards and upgraded it to the latest IOS 8.1. I was on 7.12and it still wont work. Again I have no idea why this has happened. I have checked and rechecked all flexes and connections under a magnifying glass. The jack is completely dead/unresponsive and does not recognise anything. The sound works via bluetooth the ear speaker and main speaker. I have checked all the settings in sound, made sure there was no volume leveling or muting. It worked fine before as I used to use it to listen to music with a set of genuine iphone earphones. I have tried several sets including non apple headphones and I have made sure Im pusing them all the way in. Both the new jack and old jack are free of debris. The phone does not even register the earphones being plugged in and does not respond to any of the buttons being pressed on the headphones. Phone is out of warranty so cant send it in and a technical guy from apple says its most likely hardware and not software. Is it likely something on the logic board just died on its own accord or could this be a software issue. I repair phones for a living so Im not new to fixing iphones. Please help if possible.