When I installed this furnace (new) the manual suggested using a manometer to check the draft readings at the firebox at both high and low speed combustion fan settings. I got .72 inches at high speed and between .39 and .45 inches at low speed. The low speed reading was a little higher than it should have been (.25) but was within usable specs. The furnace operated just fine for two heating seasons with this low speed draft. Now I'm having trouble getting the furnace to auto start (there is another whole thread on this problem in this forum). I measured the high and low speed draft readings and they are now .72 on high and .62 on low. Anyone have any ideas what may have caused them to change? Any ideas on what the change represents? combustion blower rotating too fast on low speed? not enough air entering the firebox? too much air entering the firebox? The stove was given a thorough cleaning from air intake right thru to the final elbow in the exhaust vent. It's as close to new (as far as cleanliness goes) as possible. I'd appreciate any ideas. I've run out of my own.