[norepairguy]

Hi all ,just figured out why carrier furnace won't fire due to code 13 error. I removed front of ignition box cover with the round site glass near top furnace casing. On the right hand side of the box there is a small disc about the size of a penny with two red wires on outside of box , cleaned with finger by rubbing dust off it.Code went away quickley and furnace fired up (nice blue flame) Problem was dust on sensor. Just installed drywall in other side of basement and fine powder got through filter.So I also checked outside for bugs bees birds nests inside exhaust tube and found nothing however there was a sizable bees nest in my water heater exhaust pipe(probably avoided a situation in the near future with hot water tank).If you can do the little things yourself you may avoid a pricy bill from your repair guy.It was not hard and you feel good for your effort.