Heat error seems not an issue for me. because overheating xbox 360's is easy to detect. xbox 360's fan has heat feedback control. if the board is hot, the fans turn faster and noisy. overheating can easily be solved by replacing the thermal paste between the heatsinks.
you can check the main error code of the heat error. Fans are not the direct fix if you dont check these key parts.
CPU and GPU are the most loaded chips when xbox360 runs, they produce heat due to extreme fast current.
these are some reasons and fixes i applied on heat errors
[img width=500 height=240]http://img107.imageshack.us/img107/7561/28513850re0.jpg[/img]
Most 3RL errors happens on the asian version. due to poor soldering on the CPU and GPU chips. "cold solder joints". for a period of time when the pins are not soldered properly. it will eventualy loose contact. and your xbox 360 will detect these and report hardware errors.
IF an error is 0102. its probably the GPU at 80%, 20% on the CPU chip. these are caused by "cold solder joints".
0020 is reported unkown. but its more likely close to 0102 error.
E74 error is also another issue, where your xbox 360 displays text in black backround. this is usually cause from the GPU to the HANA chips and to the Video out connetion.
It is also related to 0102 but 100% on the GPU chip.
Heating up your 360 will not melt these joints. probably a very slight melt on the solder joints. but no guarantee, you probably melt some other parts. because you need heat as hot as a solder machine (xbox360 manufacturing plants) to melt those solder joints.
tightening the screws can also help press the chip towards the main board, thus pushing the contacts between the solder joints for connections.
But it is risky and must take caution in doing so. use your ears to hear some cracking sound for safety.
but on my case, this screw fix is effective for me up to now.