I've got a fireplace in my upstairs bedroom that I rarely use. It is a sealed unit (glass covers the gas logs). I am able to start it and when I press the wall plate switch it does fire up and will burn for about 5 minutes, and then it goes out. I mentioned this to a friend and he thinks it could be a bad thermocouple? Attached is a picture of the starter. I am a complete noob on attempting to fix this on my own but, I would like to try if it is not too difficult. Any advise would be appreciated.