There also could be a blockage in the exhaust elbow. Need to remove and clean that if you have no idea when it was last done. I'd check that before I'd check the heat exchanger.
SailorMitchSailing winged keels since 1989.
1.20.09 Bush's last day the end of an error !! Hopefully we still have a constitution and economy left by then.
"Compassion and tolerance are not a sign of weakness, but a sign of strength." The Dalai Lama
good planets are hard to find-- a song by steve forbert
I have but one lamp by which my feet are guided, and that is the lamp of experience. I know no way of judging the future but by the past.-- Patrick Henry.