do i phone 6 screens crack when they get to hot when charging?

That looks like some sharp object hit it right around the home button. I could buy that an excessively hot home button (some people are reporting that the sapphire layer will crack) could cause something like that, but you're going to have a difficult time proving that it wasn't an impact.

It is kind of odd looking though, like the impact came from the inside of the glass. It might be worth bringing in to an Apple Store and explaining how you believe it happened. They're heard it all though, so even if you are right they're going to be extremely skeptical.

seventy one wrote:

I'm wondering if the heat is being caused by a damaged and swelling battery ... and if this could cause the screen to crack. Only an evaluation by the Genius bar people will determine that.

Good point. While rare, it does happen. If the original poster thinks this happened, make a genius bar appointment.

Anything is possible in the right (or wrong) circumstances. It could be possible for runaway heat to do that (although it shouldn't), but it might also look like something hit the screen. Apple has guidelines for evaluating glass cracks for warranty replacement eligilbity.

What does it look like? Is it one clean hairline crack with no pits in the crack? When they evaluate it they'll be looking for signs of an impact such as those missing pieces in between the cracks as well as impact damage on the case near where the crack starts. If it's relatively clean with no damage like that they might repair it under warranty. If it's a "spider web" crack or there's some noticeable damage to the case it's not going to qualify, although it might qualify for an out of warranty glass replacement if it's good enough to be repaired.

Navigate this: Genius Bar Reservation and Apple Support Options - Apple

What happened iPhone 6 error-1

Something damaged the phone. Either someone dropped it and didn't tell you, or it fell. Phones will shut off before they get hot enough to damage the phone.

I'm wondering if the heat is being caused by a damaged and swelling battery ... and if this could cause the screen to crack. Only an evaluation by the Genius bar people will determine that.

That looks to me like an impact crack, as though something was dropped on it. Notice all of the lines radiate out from a single point.

Yup, looks like impact damage. And I speak from about twenty years experience supervising the repair department at a major U.S. carrier cell phone store.