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Is the tv mounted on the wall/ enclosed in confined space like an entertainment center or wide open airflow around it?
Ok, then the only reason other then normal is that the fans need to be cleaned or as well other places excessive dust inside the unit which needs to be unplugged and cleaned with cans of compressed air in a certain way. Otherwise though, it is very normal for plasma tv's to give off a ton of heat, thats just part of the results of use from them.
As well again as I stated plasma tv's always run hotter the lcd or led tv's that just comes with this type of tv, I hate to say it but if you do not like the amount of heat then your best option is an led tv or lcd next but not an plasma because all plasma tv's give off alot of heat.
If you believe there is a problem instead and do not trust my professional advice for any reason then feel free to contact any other source including the manufacture and they will explain the exact same thing that plasma tv's give off alot of heat.
Actually plasma tv's do not give the best picture........
Also 3 years is more then enough time for dust to form inside the unit.
Again yes it is very normal for plasma tv's to give off alot of heat, theres nothing wrong with them its just the result of how the tv must operate with the plasma and everything around it.
The tv's have built in heat sensors where if a fan is not cooling the unit and it is too hot a code will come up or tv will turn off, otherwise tv is operating as normal.
A plasma tv even some lcd tv's can actual heat a small room.