Hi All, Wondering if I can tap into the collective brain trust here to help me puzzle my way through a controls question - my brain is pretty well cramped up on it. I'm getting an 80-gallon pressurized buffer tank to help minimize short cycling of my Windhager pellet boiler during low-load periods and to help meet the morning domestic water spike load. The tank I'm getting is this one: http://thermomatrix.com/thermoproducts/coolfire-buffer-tank/ in the 80-gallon flavor. My plan is to 'decouple' the boiler from the zone valves by having the boiler respond only to heat calls from the buffer tank, and have a dedicated pump between the boiler and the buffer tank. The zones have their own distribution pump and zone valves and controller, and will pull hot water from the buffer tank as needed - from the perspective of the zones, the buffer tank IS the boiler. Here's my puzzle: The buffer tank comes with two sensor wells, high & low. I'd like to use sensors in both wells to control when the boiler turns on and when it turns off. When the tank is fully charged up and the boiler is off, both sensors will be reading close to the same temperature - the top sensor a bit higher of course. As the zones start to use hot water, the stratification boundary will move upward - as I understand it, if there's not too much churning from the water inlets, there will be a pretty clean temperature boundary that will move up and down the tank. That's why tall, 'skinny' tanks are preferred. I want the pellet boiler to fire up when the upper sensor starts to drop in temperature - then I know that it will be running at least long enough to charge up nearly 80 gallons of water. If I have an aquastat connected to the upper sensor call for heat when the temp drops, say 10degF, that should work fine. But I don't want the boiler to stop until the lower sensor is also up to temperature. What I need is an aquastat that uses one sensor to 'make' and another sensor to 'break'. I've looked the the various Honeywell aquastats and the T775 controllers and none of them appear to do what I'm looking for, but I admit I'm a novice in this control logic stuff so I'm probably just missing the obvious. Maybe I need some sort of relay combination to make this happen? I could try just going with a timing relay or adjustable high/low range on a single aquastat & sensor, but then I'd be relinquishing the advantage of actually knowing what's happening across the tank. Any suggestions very appreciated.