I have a furnace that when its starting up it is very choppy but then eventually gets going and runs normally. I hear the burner turning on and off and smell diesel afterward. I've tried bleeding the line of air and no air really comes out, just the flow of fuel stops and then starts up again. I have an above ground tank lying horizontally, which is half full, and there are two 1/2" lines coming off the top of it. In the spring I used the "water worm" (http://www.h2ocontrol.com/productsWaterWorm.php) to get rid of any water lying on the bottom of the tank. I also replaced the filter in case that was clogging things up. It has been very cold and it started about a week ago. I'm wondering if some ice formed somewhere in the system, but I'm not really sure. Any suggestion are very much appreciated.