Last week after 6-7 weeks of running the manometer showed .07-.08 where it usually is always a .06. Inspected the barometer, the flapper seemed to be riding lower which will give you a higher draft. I tapped the flapper and BLAMMMMM (like that chef, whats his name ?) a slew of ash dropped off. The ash was weighing the flapper down.
So now ever week , I lightly tap and try to clean the backside of the damper .
All this suggests for safety sake:
* Shut down and clean your entire system. The one match manly thing can be unfortunately dangerous if too much ash lowers the draft especially in warm weather. Inspect your pipes thru your baro, I used a cheap flex mirror with flashlight to check ash accumulation status.
* Invest in a permanent installed manometer, I have found as a newbie that it is a base line defense in suggesting something in your system is changing !
All this fights CO.