furnace ignites intermittently

Thanks, guys. The manual was especially helpful. I pulled it out and cleaned it as thoroughly as I could without tearing it apart. It wasn't as dirty as I thought it would be considering how much dust finds its way inside the Pod. Some dead bugs and dirt inside the burner area, no wasp nests anywhere. The electrode wires were a little farther away from the burner than the specs call for plus they were a little too far apart. I adjusted that and put everything back together. Getting the outside ducts to line up and slide onto the unit was the fun part. On your knees you have to torque yourself around the corner of the kitchen counter and while using your hands to line up the ducts with the furnace outlets you simultaneously push with one knee. I was grateful for yoga at that point. Once everything was put back in place it fired right up on three consecutive tries. Got my fingers crossed that it stays that way. Thanks again for your help. 

However, if something like a mud dauber nest is blocking the thermocouple, the furnace might not be registering that it is lit and shuts down.