1. 3 way valve and O.S.A. reset. 2. Single boiler piping schematic. 3. Single boiler with 3 way valve piping schematic. 4. Dual boiler piping schematic (pumps on outlet). 5. Dual boiler piping schematic (pumps on inlet). 6. Primary, secondary piping schematic with 3 way valve. 7. DDC interface.