Heating/cooling changeover via BACnet/Modbus (P02)

BACnet/Modbus provides heating/cooling changeover information; but only if the control sequence is set to automatic heating/cooling changeover (P02 = 3) and no local input (X1) is assigned to this function.

Heating/cooling changeover

Required information is unavailable (e.g., due to data communication problems, power failure, etc.), the thermostat operates in the last valid room operating mode (heating or cooling).

Automatic heating/cooling changeover via changeover sensor (P60) (RDF4..BN)

If a cable temperature sensor (QAH11.1 + ARG86.3) is connected to X1 and P60 is set to 3, the water temperature acquired by the changeover sensor is used to change over from heating to cooling, or vice versa.

  • When the water temperature is above 28 °C (adjustable via P65), the thermostat changes over to heating and remains there until the temperature drops below 16 °C (adjustable via P64).
  • When the water temperature is below 16 °C (P64), the thermostat changes over to cooling and remains there until the temperature exceeds 28 °C (P65).


Operating mode

Cooling mode


Water temperature

Heating mode


The setting range is 10...25 °C for P64 and 27… 40 °C for P65.

Changeover switch (P60/P62)

An external switch for manual, remote changeover can replace the QAH11.1 cable temperature sensor for automatic heating / cooling changeover:

Contact open  ⇨  Heating mode

Contact closed ⇨ cooling mode

The sensor or switch connects to input terminal X1/D1, depending on input commissioning (P60/P62).

An external switch is connected to X1/D1 (P60/P62 = 3) to change heating/cooling mode remotely.

See also Multifunctional input, digital input.

Manual heating/cooling changeover (P02)

  • Manual heating/cooling changeover means selection via mode button on the thermostat by repeatedly tapping the button until the required mode is displayed.
  • In manual heating/cooling changeover (P02 = 4), the heating/cooling mode cannot be changed via bus/changeover sensor/switch; it remains in the last mode selected locally.

External temperature sensor (P60) (RDF4..BN)

The thermostat acquires the room temperature via built-in sensor or external room temperature sensor (QAA32) connected to multifunctional input X1.

Inputs X1 must be commissioned accordingly. See Multifunctional input, digital input.