I have a conventional central boiler 6048 and I believe I have a creosote issue. Yesterday the stove wasn’t getting any draft and water temperatures were in the 90s so first of all I checked the door draft and that was working perfect so then I moved to the inspection cover at the rear of the unit and removed that expecting the tee to be plugged, nope so logically I assumed the chimney was plugged. Nope wrong again. Is it possible that there is a blockage somewhere between the firebox and where I can’t see a couple feet in from the back inspection cover???