Fireplace

It could be an overtemp switch cutting it off. This has been discussed on the Open Range forum and is fairly common. I'm sure other manufacturers build them in the same way. The fireplace (electric heater) is set back in a cabinet and very little air gets to the back side. It heats for a while and then stops. After it cools down it will come back on. The easy fix is to add a couple of air vents on either side of the heater. Most just drill a couple of holes in the wood and cover with a floor register to make it look nice. I have not had a need for our fireplace heater yet but I plan to add the vents before I start using it. If yours will come back on after a cooling period you might want to look into this fix.