Don't know if this will help, but I'm getting deja vu reading your post. Rather than figure out your system, I just want to pass along my experience in case it gives you any help troubleshooting. We bought our house last March and only ran the woodburner a week so it wasn't until this October that I started to analyze how the whole system worked. The first thing I noticed was, similar to what you're describing, even with the woodburner blasting our gas furnace was coming on all the time. Here's our set up: a Mahoning woodburner (290 gallons) sends hot water into a SuperStor Ultra indirect fired hot water tank in the basement. This hot water tank has a single wall heat exchanger, so heat is transferred at this point from the wood boiler water to the water for our baseboard heating system. The pump from the OWB to the heat exchanger runs continuously, and we set the OWB at 190 degrees, which results in water temps between 165 - 175 degrees (aquastat on the OWB is screwed up a bit). The heated water then exits the SuperStor tank and enters a Smith gas fired boiler, from there up into the house to do its job via a second circulator pump.
First we had a heating/cooling guy come over to clean the gas furnace and try to make sense of the system for us. On the way out, he noticed one of the numerous valves in the maze of copper piping in the basement was closed - it just happened to be the valve that allowed the hot water from the heat exchanger to mix with the water from the gas boiler. So first lesson learned: look for simple solutions. This seemed to help, but we were still hearing the gas boiler come on nearly every time the house thermostat kicks on, although it wasn't staying on as long as before. I spent some more time in the basement watching the furnace cycle through, and here's what was happening:
The Smith boiler has an aquastat which measures the temp of the water inside the gas boiler reservoir. The minimum setting for this aquastat is 180 degrees, so that's where we set it. When the thermostat in the house turns on, two things happen: the circulator pump starts pumping water through the system, and the aquastat in the gas boiler kicks on the gas furnace if the water temp in the boiler reservoir is low enough. The problem was, because the water inside the boiler had cooled down to 130 or 140 degrees between cycles, the gas boiler ALWAYS came on, even though I had hot 175 degree water waiting in the tank with the heat exchanger. Eventually, the pump brought this hot water through the gas boiler reservoir on its way up into the house, so running the wood burner at 175 degrees shortened the amount of time it took the gas boiler to raise the water temp in the reservoir from 140 to 180 degrees from about 10 minutes to 2 or 3. But the gas boiler was still coming on, so the solution: I unplugged the wires on the gas boiler aquastat and plugged them into the aquastat on the indirect fired water heater tank (in fact, eventually I just unplugged the aquastat altogether). So second lesson learned - don't let your aquastat fire based on cold water sitting in a reservoir between cycles, make sure it's measuring the temp of the water that's actually doing the work in the system. I'm not sure if this could be happening in your case, but it's something to think about. Our gas boiler doesn't fire at all anymore, and we're heating a poorly insulated 1870's 2600 square foot farm house on 10 - 12 hour burns, so it can be done.
First we had a heating/cooling guy come over to clean the gas furnace and try to make sense of the system for us. On the way out, he noticed one of the numerous valves in the maze of copper piping in the basement was closed - it just happened to be the valve that allowed the hot water from the heat exchanger to mix with the water from the gas boiler. So first lesson learned: look for simple solutions. This seemed to help, but we were still hearing the gas boiler come on nearly every time the house thermostat kicks on, although it wasn't staying on as long as before. I spent some more time in the basement watching the furnace cycle through, and here's what was happening:
The Smith boiler has an aquastat which measures the temp of the water inside the gas boiler reservoir. The minimum setting for this aquastat is 180 degrees, so that's where we set it. When the thermostat in the house turns on, two things happen: the circulator pump starts pumping water through the system, and the aquastat in the gas boiler kicks on the gas furnace if the water temp in the boiler reservoir is low enough. The problem was, because the water inside the boiler had cooled down to 130 or 140 degrees between cycles, the gas boiler ALWAYS came on, even though I had hot 175 degree water waiting in the tank with the heat exchanger. Eventually, the pump brought this hot water through the gas boiler reservoir on its way up into the house, so running the wood burner at 175 degrees shortened the amount of time it took the gas boiler to raise the water temp in the reservoir from 140 to 180 degrees from about 10 minutes to 2 or 3. But the gas boiler was still coming on, so the solution: I unplugged the wires on the gas boiler aquastat and plugged them into the aquastat on the indirect fired water heater tank (in fact, eventually I just unplugged the aquastat altogether). So second lesson learned - don't let your aquastat fire based on cold water sitting in a reservoir between cycles, make sure it's measuring the temp of the water that's actually doing the work in the system. I'm not sure if this could be happening in your case, but it's something to think about. Our gas boiler doesn't fire at all anymore, and we're heating a poorly insulated 1870's 2600 square foot farm house on 10 - 12 hour burns, so it can be done.
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