Share your experience!
I have only had the phone a few weeks and now when the headphones are plugged in the sound still comes out of the phones speakers. I have tried different headphones and it is the same. When I plug the headphones that came with the phone in it says 'headset not supported' . Any help would be appreciated
@SkiSwitch first thing i would check is that there is nothing ie dust/lint etc stuck in the actual jack hole....but don't go prodding around with a sharp object, is the headphone jack seated tightly in 
I have looked in the jack socket with a small flash light and it seems clear. The jack clicks in firmly when you push it in
Hi @SkiSwitch, I am sorry to hear about this.
Do the headphones feel loose in the jack at all? Does it wiggle?
Do you have the same issue in safe mode?
Hi SkiSwitch,
I have experienced this before with my Xperia Z5 Premium, a few times. Now, I am using Xperia XZ Prem.
I just wanna share my experience because maybe this can help. When my Xperia Z5 Premium was repaired, the diagnosis was loose headphone port. So they replaced the headphone port with a new one. After that, it works fine again.
If you want a work around for this and want to hear the sound from your phone, you can use the application Soundabout from google playstore. Note: it doesnt fix the hardware problem, if there is.
If you want a sure solution for that, I would suggest that you bring the mobile to the nearest Xperia Support Center in your country.
Thanks and Regards 
Thanks for the fast respose guys. It looks like a hardware issue so will try and get it sorted through xperia service centre