We have been using our fireplace (Dimplex model DF2603) as a heater on and off for the last few weeks, mostly on. I started to smell electrical wire burning and traced it to the fireplace. I took it apart to find that where the power cord came into a terminal block it had burnt the wire and melted part of the block. Not sure what would have happened if we had not been at home, I hope it would have fried the 120 power cord and just shorted out. I guess I don't really want to know.
My only suggestion is to take the top off your fireplace and make sure the screws are tight on the terminal block. The factory sent out replacement parts, the wrong cord, but I made it work. They said this is the first time this has happened, I wonder? The first picture is the top of the fireplace turned upside down and then a close up of the terminal block.