I have an older model sears searies 600 model number 867761833 heater. The pilot light is on but the furnace will not start. The programmable thermastat is only a year old but I put new one in any way. I also changed out the thremocouple. A few weeks ago I noticed that it would start then stop a few times before it would kick on. Any suggestions since its minus 2 outside :-(

Will the blower run if you switch it to "ON" on the thermostat?

Waiting for your response to hvacservicetech_07's question, and we will try to help, one step at a time.

After some more investigation I found a blown fuse that I did not know was there. I replaced the fuse and found a wire that had melted grounded out to blow the fuse. Now the furnace works but one of my 4 burners is not burning correctly, (I am assuming it needs to be vacuumed out). It is near the wire that grounded out. The instead of being a nice upward shooting flame it kind of goes every where. I will have to leave it till morning though since I have to work grave yards.

Sounds like the orfice and burners could use a good cleaning. Try removing the orfice on that burner, it may be partially plugged.