My raspberry pi gives me heat warning after 5 minutes it is turned on. I tried heat sink on my Pi and the only difference it made that it gave me warning after 10 to 15 mins rather giving it the moment it was turned on. Now i used fan along with heat sink. It dropped the temperature to 56 degree celsius. This is a quite abnornal behaviour. I am not running ANY program on pi and CPU usage is always 1 to 7 percent.
This is likely caused by a faulty (over-voltage) power supply, static damage, over-loading the 3V3 rail, over-loading a GPIO or some other wiring mistake.