Rob R. wrote:The calibration and performance of thermocouples can vary. Adjust your ashing control so you have a layer of unburned coal on the very top of the fire column, with burning coal visible between the unburned pieces. If you get puffbacks, reduce the ashing temperature.
Aquastat settings sound fine.
I agree with Rob on this.
Do not be concerned so much about a certain number setting or matching someone else's number...do it by what position the fire is in when viewed through the view port.
Another thought on outfires, even with the best chimney draft, the combustion air needs to come up through the ash from grate level on AA and AHS units.
With that said, draft/air will take the path of least resistance
Burning a coal higher in ash can restrict air on even a unit with induced draft, as it will block or plug the spaces that the air needs to pass up through to re-ignite the dormant red coals perhaps near 12" above.
This likely would also be a cause for excess un-burnt coal in ash pan and since the ashing controller never gets to sense the fire position/temperature it keeps on ashing to no end causing high daily coal use.
If ash is restrictive enough, the air/draft from below will be reduced and the air will come from anywhere it is less restrictive. Anyone who has had their hopper on an ASH run empty or an AA auger exposed in the bin knows this...the fan will pull air down through hopper or up through hollow auger, and little if any air up through from the ash grate area.
It sounds like this supply of coal worked well during the colder seasons higher boiler loads and is only a problem when latter experiencing the lighter boiler loads.
My .02 cents, "You really need to get a few bags/buckets of a different coal to see what a difference that will make".
Making a whole lot of adjustments/changes would not make up for a draft problem which may not be a chimney problem.
I would check that manometer...a little light suction should prove tube is clear and poke a bit into flue fitting.