I have a 5 yr. old dunkirk xeb3 boiler. This year on starting I noticed a smell of burnt gas coming out from around the draft inducer housing. I checked housing and gasket, both seemed fine. Fan only runs for approx. 5 seconds before ignition, and shuts off right after flame stops. Could this be faulty fan or switch? Boiler works except for odor. Any ideas or help is appreciated.

Check the vent or flue pipe for restrictions. If it is plastic pipe going outside you might be surprised what you may find. Ice,birds etc.

Vent pipe is clear. Horizontal steel venting clear to outside. Thanks

At this point, I think its time to have a pro in to check for carbon monoxide. IF you are smelling something out of the ordinary, its best to be safe and have it checked out. Wish I had a better answer for you, but with smells, it all guesswork. Good luck and please let us know what you find.