The Mixing Expansion Module 444 is designed to operate a mixing device within a hydronic heating system as part of a tekmarNet (R) control system. It is capable of controlling a mixed system pump and six optional outputs for mixing: a variable speed injection pump, a floating action actuator, or an analog 0-10 V (dc), 2-10 V (dc), 0-20 mA, or 4-20 mA signal.