Q: My Iphone 4 is warning it needs to cool before using what may be the problem

Hi duncanfrommombasa,

Thanks for using the Apple Support Communities!

I understand that you are receiving a temperature alert on your iPhone and know how concerning this alert can be. The following article discusses why this may happen and what you should do if you see this warning. Please read over it for more information. 

Keeping iPhone, iPad, and iPod touch within acceptable operating temperatures - Apple Support

Best!