iPhone 6 recently running hot

Hello,

I've had my iPhone 6 for the past 6 months and it's been running fine until about a week ago when it has started to get really hot at times when not in use. The battery consequently runs down really fast even though I make sure all apps are closed. I haven't changed the way I've been using it since I purchased it (I have wifi and bluetooth on all the time) and I have a tech21 impact rubber case since day 1. The phone has the last iOS update as well.

I had the same problem on my former iPhone 5 and it turns out the battery was faulty and changed under warranty. Not sure if I have the same problem with my 6 now...

Has anybody else had this issue lately? What can I do to solve this problem?

Thanks.