Sony xperia zx keeps overheating

The sony i had used for 3 minths started overheating. Agter 6months it got replaced with a new one as they couldnt fix it. So the new one lasted for a few months and now sitting with exactly the same thing... overheating. So now my phone needs to go in to vodacom shop for repairs again. Why do a person needs to keep taking phones in for repairs. I dont even play games on the phone. I cant take photos or videos then the phone shuts down due to overheating. It looks like its a sony thing and wasnt just one dud phone.