Thanks for the welcome, ngzcaz.
The "water use reduction" fix I did is a simple 1/2 inch PVC cap. I sanded the exterior of the vent line nice and smooth with 220 grit sandpaper so the cap would slide on and off easily. I drilled a 1/8 inch hole in the center on the cap to allow the tank to breathe with atmospheric pressure changes and water volume changes that occur with changes in water temperature. The cap slips on with very little force and will come off if the water were to boil and build pressure. Each week when I do the ash cleaning I pull the cap off (to be sure it isn't getting stuck from sitting in one place too long) and top off the water. Then I slip the cap back on. Since I started using the cap I only have the fill water on for a second or two, before I had to let it run for 15 to 20 seconds to top off the tank.
I'm not really hung up on the exact temp of the water as long as the controller is keeping it in a reasonably tight range and I am getting hot air and hot water in the house. To check the actual water temperature I insert a long probe on a digital thermometer into the vent tube far enough that it is in the water inside the tank. I normally see a water temp that is within 3 degrees or so of the temp shown on the controller and wireless remote thermometer. The reason for this is that I insulated the crap out of the place I installed those probes. First, the probes have thermal conductive grease on them, then 1/4 inch blue foam insulation over them, then fiberglass filling the factory hole for the temp controller, then 1/4 inch blue foam over that and extends about 2 inches beyond the hole all around to hold in the fiberglass , then 3 inches of fiberglass bat over all that. With the digital controller set to come on at 159 and off at 161 degrees F the draft fan cycles for a short time often. I'm sure there is some lag in the system due to the 1/4 inch of steel between the water and the probes, but if you hold the temperature fairly constant for a period of time the, I'm guessing 10 minutes or so, the extra insulation will allow the heat to soak through the steel and the temperatures to equalize. Once equalized the response to small changes in temperature is good enough to control the system. This results in a very steady burn as long as there is a constant load from the house. My wife thought I was nuts, maybe I am, when I sat and watched the furnace run one night for almost an hour and a half. It was much more relaxing than watching the tv.... Anyway, the outside temperature was about 18 degrees that night and the house thermostat was kicking on for about a minute and off for about 8 minutes in a steady cycle. The furnace draft blower was kicking on for about 4 or 5 minutes once about every 3 house cycles. The temp of the furnace was cycling from 159 to 161 and never strayed from that. I use a set back thermostat in the house. The normal temp is 72 degrees and it sets back to 65 degrees during the day while we are at work and school. I have it step up to 72 about a half hour before we get home and it never fails to be there when we walk in. I have a digital thermometer in the house that records the high and low temps and it does get down to 65 during the day when the outside temps are in the low teens or less. The furnace is usually at around 145 to 150 and recovers within a half hour after we get home, even with the hot water useage that occurs during that time - not bad for a sudden 7 degree jump in the house temperature. Another example is when my son takes a much too long shower. The furnace temp will drop to around 153 degrees or so and then recover. When he finishes the shower it will overshoot to no more then 164 and then settle back down.
I feel I finally have the temperature control of the furnace working the way I think it should and it is very solid in it's response as long as there is wood in it and I keep the grate and chimney clean. Now I want to work on the chimney creasote problem by installing the insulated chimney and then insulating the entire water tank much better than it is to reduce my wood useage and extend my run times. There is a single thin sheet of (probably wet) fiberglass insulation that came with the unit to place under the water tank. Even with that I noted that all the 1 inch of snow we had Monday was melted out to about 4 to 6 inches from the furnace with an outside temp of about 20 degrees.
As it is I only fully load the front half of the firebox over the grate, that is the firebox is only half full of wood, once a day in the evening with the average daytime temps in the 30 to 40 degree range. Below that I throw in 4 to 8 splits in the morning depending on the predicted high for the day and how much sunshine we are supposed to get to make sure it stays hot. Above that range I only about half fill the front of the firebox once a day, that is the firebox is only 1/4 full. How much wood is left and how much I have to add depends on whether the day was very sunny or not. When it is sunny the solar panels tend to keep the temp up and the blower off all day long so there is lots of wood left at the end of the day.
I hope that adequately answered your questions!