Boy did I mess this post up !!! I guess I should have my morning coffee BEFORE I post anything... !!
My brain sure wan't 'in gear'
Correction: replace the line: 'Manometer, at least the Dwyer Mark II'. With the line: ' Barometric dampers, at least the Field controls recommended for coal use'. Manometers, at least the Dwyer Mark II
have two slots for the weight, one marked H, the other marked V... this is for when the manometer is in a Horizontal run of flue pipe, or in a Vertical run of flue pipe... take a look at yours, maybe you have it in the wrong slot?? if yours is the same design???
It's been done many times, by installers that should have seen it during installation..
Since your chimney was in need of cleaning, have you cleaned the firebox, and heat exchanger inside the unit ever ??? They collect fly ash too, and need cleaning to stay efficient.