heat gun can mess up your board if you are not carefulUsing 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.