mdhorvath wrote: Any ideas?
1) Make sure the L4006A is set up as the "operating limit" aquastat, and the L4082B is set up as the "high limit" aquastat (as this is correct, albeit being contrary to the wiring diagram, and for this I urge you to not accept my word, but rather call AHS and confirm it).
2) Bump up the dump zone to 215 or even 220 degrees.
3) Lower the ash grate motors initiation temperature to 125-130 degrees (or perhaps even to 120 degrees), to increase the amount of ash residing beneath the coal in the anthratube and thin out the fire. This should inhibit the air that is being drawn up through the ashes and into the coal.
4) Make sure the flapper is opening only about 1/4" when the fan shuts off. More that this and your over the fire air is going to be increased.
5) Make sure the flapper is resting solidly closed against the port opening to the anthratube when the fan is on.
6) Make sure the boiler has been fully de-aireated and it doesn't have a big air pocket in it.