I have a gas fireplace manufactured by Superior. It is model DS-36TN. The unit was in the house when I bought the place in 2002 and worked fine for the past several years.

About 2 months ago it started cutting out after being on for anywhere between 20 min and 1 1/2 hrs. I always turn the wall switch to the off position when it cuts out, sometimes it will come back on if I attempt it a short time later, other times the pilot light has gone out and requires relighting. There is no external electrical power that goes to the unit through the switch, the switch only controls the gas valve open signal from the thermocouple voltage (I think).

Please help

Jeff

Could be a plugged pilot orifice. It could have some debris in it.
Make sure the pilot height is correct especially the area where it is supposed to contact the thermocouple.
Could be the high limit safety control. (check the flue exhaust for obstruction)
Check air intake if it is a concentric air and flue combo.
It could be the gas valve but I would check all other items first before replacing. Hopefully someone left the book for the fireplace if not you may need to obtain one to find out the location of the parts to test.

Now it could also be ventless and if it is I suggest professional repair. There is a oxygen depletion sensor as a life safety device and that needs to be tested when serviced. LOOK at there web site below.

Fireplaces and Stoves by Superior

Jeff, did you ever find out what the problem is? I have the same fireplace with the same problem.