do you see him by the heater at all? thats obviously the only way he would get burned but most of the time, provided his stress is down and the water quality is good, it will heal naturaly without the help of meds. i had the same problem with a powder blue, it went away in about 3 days and the fish is still living. its been about a year since that. just keep the water clean and monitor closely and if you need to you can get a cover that will go over the heater, and prevents occasions like this.