I was not aware that standard buffer tanks need/use an aquastat. I thought that buffer tanks are piped using the four ports and the cavity served as a storage facility. I'm guessing the boiler circ pulls from the tank to maintain flow for the boiler while the zone circs pull from the tank to satisfy the zone stats. I was thinking the aquastat was used when and if the tank functions as an indirect water heater. Am I way off base here ? Thanks.