I bought a used Jotul GF 400 DV. The sticker underneath, on the burner, says Natural Gas. But there's also a Propane conversion sticker on the rear serial number plate. Is there any way to tell whether it's been converted (or maybe converted and then converted back) short of taking it all apart? The people I bought it from have natural gas at their house, so I assumed that's what they were burning, but I'm not certain. (The craigslist ad is gone, so I no longer have their contact info -- also, I guess it's possible they were trying to run it on natural gas even though it had been converted to propane). Can I try to burn propane and see if it works? What would happen then if it's set up for natural gas?