The HKM3 heating circuit module enables the control of an additional heating circuit. The controller connected can be extended by a complete weather-compensated heating circuit by connecting the HKM3 via the VBus®. The HKM3 is equipped with 6 sensor inputs, one of which can be used for the optional RTA12 remote control. For the connection of a mixing valve and a heating circuit pump, 3 semiconductor relays are available, as well as one potential-free relay for backup heating demand. In combination with the controller connected, the HKM3 not only controls the basic functions of the heating circuit and the DHW priority, it also has an antifreeze function and a blocking protection for the heating circuit pump.