I have been following this thread loosely. Just a note on my experiences this year. I found that the K-6 works much better on a mix of 20% rice in the buck. I needed more air with the buck to keep the fire burning and a longer timer setting. This was over heating the boiler and activating the dump. Now with the rice mix, I have it dialed in to idle just fine.
The AA130 did not overheat when I tested it this spring. However, after insulating the boiler shell, the water temps shot up on sudden shutdown. I have adjusted the aquastat a little and gotten the dump zone hooked to turn on the boiler circulator on over temp. It is working fine, but the workshop is a little warmer due to increased hot water circulation which partially defeats the savings from the insulation on the boiler. I will be playing with it a little more.
My observation that has been eluded to here. The K-6 has 50 gallons of water in it and takes quite a bit of heat to over heat. The Axeman Anderson 130 has 27 gallons and responds much faster due to the lower mass. The Leisure line only has 12 gallons of water in it, making it an extremely low mass boiler for a solid fuel boiler. Extreme measures may have to be taken with the LL boiler to minimize dumping. This means setting up the system expansion to allow the boiler to go to 240 degress before activating the dump. It will also require the low setting on the aquastat to be at 140 or a little lower.
Part of the problem may lay in the simple system dynamics. Coal boilers and thermostats are controlled as two position devices. They are on or off. This means the thermostat calls for heat, the boiler burner is fired until the thermostat is satisified or the high or operating setting on the aquastat is made. In the mean time, the fire has been fanned and fuel added in attempt to reach the hi limit. The high limit setting is typically what is needed at system design, which is only 2% of the time on average. This fire now must die down. One possible solution is to integrate a indoor-outdoor reset in the system. This would automatically limit the upper boiler water temperature based on outside air. If properly adjusted, this could have a tendancy to cut off the burner before the house thermostat was satisfied, allowing the fire to coast as the themostat was satisifed. Of course this would not be a 100% solution but certainly would help.
Another issue is with larger mass boilers, there is less need to dump because the heat is lost through the jacket. While you can say that the dump zone is not activated as much, you still loose heat to a less desirable area such as the basement. You might better use the house as a dump zone rather than loose heat to a normally non-occupied area.
When I had my wood boiler going, it dumped to the house. This was fine, as the house might be a little warmer than the thermostat setting at times. My wife did not have any complaints about that setup. So, my suggestion is to dump to the house. In a single zone system like my wood boiler was, a high limit aquastat wired in parallel to the house thermostat would activate the boiler pump if the water temperature climbed above it's setting. This would dump heat to the house and let the boiler stay at idle.