Aqotec RM360 over Modbus, Part 4: External Room Temperature for HC2

This fourth part covers the one write that is intentionally periodic: sending an external room temperature from Home Assistant to the AQOTEC RM360 for heating circuit 2.

The Home Assistant side is simple, but it only makes sense after the RM360 has been configured for this operating mode at the controller itself.

What gets written

For heating circuit 2, the RM360 expects the external room temperature here:

The controller expects a fresh value at least every 20 seconds. If the value is missing, the Modbus room value is discarded and the controller falls back to the local room-sensor input or the configured fallback behavior.

Important: this register cannot be read back with FC3. Do not create a read sensor for register 46002.

Home Assistant helper

Use an explicit enable switch so the periodic write can be disabled quickly.

input_boolean:
  rm360_hc2_room_temp_enabled:
    name: "RM360 HC2 Room Temperature Enabled"
    icon: mdi:home-thermometer

Home Assistant automation

- id: rm360_hc2_room_temp_write
  alias: RM360 HC2 Room Temperature Write
  mode: single
  triggers:
    - trigger: time_pattern
      seconds: /10
  conditions:
    - condition: state
      entity_id: input_boolean.rm360_hc2_room_temp_enabled
      state: "on"
    - condition: numeric_state
      entity_id: sensor.living_room_temperature
      above: 5
      below: 35
  actions:
    - action: modbus.write_register
      data:
        hub: rm360
        slave: 1
        address: 46002
        value: >
          {{ (states('sensor.living_room_temperature') | float * 10) | round(0) | int }}

Use your actual room-temperature entity. In my setup this is the living-room temperature sensor.

RM360 service-menu checklist

The following steps are done on the AQOTEC RM360 controller, not in Home Assistant.

Before changing values, write down the current settings.

1. Open the service level

On the controller:

1. Navigate with the right-arrow key until you reach the service level.
2. Press ESC to open code entry.
3. Enter the service code for level 3.
4. Open the service / parameter menu.

2. Set heating circuit 2 to room thermostat mode

Parameter:

• 3 – Heating circuit 2
• Setting: Room thermostat

In this mode, heating circuit 2 is switched off when the room temperature rises above the current room setpoint plus hysteresis. When the room temperature falls below the setpoint again, heating circuit 2 is enabled and controlled by the heating curve.

3. Configure the remote-control input

Parameter:

• 159 – Remote control HC2
• Setting: Contact open on

The FBS/GND input must be open, or at least not blocked by an external contact. According to aqotec, this setting is required for using the room value transferred via Modbus.

4. Set the room target temperature

Parameter:

• 150 – Room target temperature HC2
• Suggested start value: 21.0 °C

This is the base room target. General and HC2-specific day/night corrections are added to or subtracted from this value.

5. Set the room-thermostat hysteresis

Parameter:

• 163 – Room thermostat hysteresis HC2
• Careful start value: 0.5 K

Example with a 21.0 °C target and 0.5 K hysteresis:

• room temperature above 21.5 °C → HC2 is disabled
• room temperature below 21.0 °C → HC2 is enabled again

0.5 K is a reasonable starting point, not a mandatory value from the documentation. If the heating circuit switches too often, increase the hysteresis a little.

6. Keep the room-temperature offset neutral at first

Parameter:

• 994 – Room temperature offset HC2
• Initial setting: 0.0 K

Only change this if the room value used by the RM360 is consistently different from a checked reference thermometer.

7. Check operating modes

These modes must not block heating circuit 2:

• overall operating mode: Auto or Heating only
• HC2 operating mode: Auto

The following functions still apply:

• heating / setback time program
• outdoor-temperature cutoff
• buffer undertemperature cutoff
• domestic-hot-water priority
• frost protection

The room thermostat does not override these safety and enable conditions.

Commissioning test

After the RM360 settings are checked:

1. Keep the Home Assistant enable switch off.
2. Send one safe manual test value, for example 214 for 21.4 °C.
3. Check the RM360 display / parameter view.
4. If the controller accepts the value, enable the Home Assistant automation.
5. Watch at least a few 10-second cycles.
6. Disable the automation once and confirm that the RM360 falls back as expected.

This is the only periodic write in my RM360 setup. Normal setpoints and corrections are written only when the user changes a Home Assistant helper.

Series navigation

Previous step: Aqotec RM360 over Modbus, Part 3: Safe Writes and Automations