Anything come to mind other then incomplete combustion.
I'm going out tomorrow on unit that the people say has a smell of L.P. at the flue pipe.
Other companys have been there, with nothing really to report as to the cause.
1st thing i'm going to look at is the pressure, but i'm sure thats been done.
This unit is about 1 1/2 yrs old.
I don't knnow if it's a 1 or 2 pipe, but if it's a 1 pipe.
and getting combustion air from the house, could that be a result ?