hi folks, something to try if you have double wall pipe and a sweet smell. I had never run across that in all my time in this industry, but just approx 2 weeks ago we had a customer with that same smell, we tried everything, manufacture couldn't help us, so i finally sent a crew to completely change out the pipe. The pipe was double wall pipe with an extendable section, when the installers removed the pipe they found that enough dust had blown up inbetween the pipes to build up and begin to char slightly. We had taken the pipe to fairly high temps thinking the problem was just burn off, but it had this sweet smell that totally confused us. Replaced the pipe and the smell went away. The customer had modified his blower & my tech felt like the fan was blowing to directly on the pipe. Hope this is helpful to someone, would love to hear back from some to see what you find.