Hello, when temp led is on it is a way to protect the unit from overheating, Inside the PJ there are several fans (usually3-4) to cool down the temp of the power board, lamp , dlp chip etc. First do visual inspection of outer visible fans , maybe some are stuck. Then you can try using vacuum cleaner to clear the dust inside. If this don't help deeper cleaning is needed with opening the unit. If yuo are not familiar with electronics and due to risk of electric shock, please do not open the unit by yourself, and visit proper service center.
Of course upper suggestion is only the one of common cause for described problem.
Hope this helps.