Looking for replacement parts for a Majestic Gas Fireplace??

http://www.majesticproducts.com/Customer-Care/User-Guides-Manuals.aspx

If you are able to , open the burner box , the igniter has a thermocouple ( might look like a thick wire that would be in the flame if it were on). If it gets corroded or junked up it will not register the flames presence and will shut off the gas). Take an emory cloth and polish it. Hope it helps.

Does your fireplace have a thermostat connected? If so, that may be why the pilot stays on and the burner goes off. Otherwise, it could be a bad thermopile. If that is the case, I recommend you just replace the entire pilot assembly. It is an older model and manuals can be hard ti find. If you still have trouble, I recommend you contact a local certified gas appliance technician.

Check a safety device called thermopile which the two wires connected to the unit needs to be around 500mV to open gas. This part is between 35-50$ If that is not the problem, you may need to replace unit gas valve.

Unfortunately, any replacement parts for a 1979 Majestic Fireplace are long gone. Majestic went bankrupt 4 or 5 years ago.

Sorry, I wish I had better news. But, it is what it is. Thanks for choosing FixYa.

The Insta-Flame burner was a product of Majestic Fireplace/Vermont Castings, which went bankrupt and is no longer in business. However, Monessen Hearth, bought the gas fireplace and gas log part of the business. But, their new model numbers don't match up yours. If you could provide me with how old your fireplace is , the full Model Number and Serial Number. I may can help you.

Please advise.

Yes, hopefully changing the thermocouple (skinny sensor) or thermopile(fat sensor) would do the trick.
Start with these fairly inexpensive repairs first.
Unfortunately if the honeywell valve is bad a new one can be expensive.
Also it is hard to order parts from Majestic, they just went bankrupt, not to long ago and Martin is taking them over. You might look for your valves model# and check online for other suppliers of that model# or ask for a compatible Direct Vent gas valve that's not as problematic. (eBay and HVAC dealers, etc.)
FYI:
You said it's been about 5 years, you might decide it's less of a hassle to have new gas fireplace installed. Martin and Empire are probably two of the best, with 5 year parts and labor warrantys.
Hope you find some success in your endeavor.