The dryer stopped heating so I replaced the ignitor. It fired up and worked for most of one load before the air began to cool off. Now there is no heat even though the drum turns and the fan works. Is there something else I need to replace? The flame sensor? (I don't understand how it can sense for flame for heat allowing the gas valve to open. Doesn't there have to be gas first to make a flame?) The thermal fuse? The thermister? The hi-limit thermostat? The sensor wiring harness? This has been a great washer/dryer set with high capacity and efficient water use. I'd like to keep it going. Can anyone relate to this problem I'm dealing with? Thanks.