Using a heatgun is probably THE worse thing you could do. Yes it may work for a few days, but in reality you're just doing more damage to the already stressed components.
Have it looked at by a professional or somewhere that offers a reflow/reballing service. YES it is £££ $$$ but how much is a new PS3? How much is a 2nd hand one? How much do $ony charge for repairs? I think 40-50 is a reasonable price, and IF done properly your console will live on for a fair few more years.
heat gun can mess up your board if you are not careful
If you use liquid flux with the heat gun the fix will last much longer. My son and I used the heat gun method a few times without flux and it would always YLOD after a few hours of intense playing. BUT after using the flux it has been over 17 months WITHOUT a YLOD.
The key to using a heat gun for any type of repair is preparation and patience. There is a difference between the heatgun used to strip paint off of a car and the one used to work on PCBs. As was mentioned above, pre-heating the entire board to prevent warping is a must. You also need to carefully cover parts like capacitors and connectors with a heat shield like foil to prevent damage. Take your time and SLOWLY heat the components necessary to re-flow their solder points.
If you get is a hurry you'll turn your board into a taco, and ruin any chance of fixing it. Lastly, for the love of god, never NEVER put it in a household oven. Yes, there are ovens for PCBs, but they are specialized for exact temperature control and heat profiles to prevent damage. Attempting to "bake" your board will only result in a melted pile of plastic.
I have repaired many many xbox 360's with RROD using the correct heatgun and a lot of practice. You can do it, if you take your time.
Exactly what im talking about mushy409, a lot of people think of a Ryobi 1100 degree automotive heatgun when this topic comes up, but a good rework station like that is exactly what I use and is, IMO, the only way to do it right.
you would probably be better off using a liquid soldering flux that you can get at any radio shack i beleave and following the directions of it using a heat gun as mushy409 said is the worst thing you can do bc if you over heat it it dead, if you even bump the table the mobo is sitting on it dead, pretty much unless you do stuff like that for a living your gonna kill it wat beyond repair try selling it on craigslist for parts or ebay and get yourself a new ps3.
As i mentioned in my last post, i used the heat gun and gilksys guide and that brought my PS3 back to life after YLOD.
A couple of days later i noticed a local computer vendor had a half price day for PS3 repairs. Knowing that a reflow YLOD fix wouldn't last, he re-balled the GPU for £30 which includes a 3 month warranty.