My SolarFusion SF30NT keeps shutting off. It'll be going full blast trying to keep the room warm, and will just randomly shut off. When it does, it makes a loud ticking noise, like something is dropping inside it. Does anyone know why this is? My first thought was that there is air in the gas line, but this is beginning to happen quite frequently (every couple days), and today, I haven't been able to get it to stay lit for more than 3-4 minutes at a time for the last couple hours. Our house is freezing, and we're running space heaters to keep us warm. Can anyone help me? Thanks!