Geo9 Modbus Register 1901: HeatPump Return T16

Technical Definition

The register HeatPump Return T16 at address 1901 is used to monitor heatpump return t16 on the Geo9.

• Protocol: Modbus RTU
• Data Type: S WORD
• Unit: °C
• Access: Read Only

How to Read (Python pymodbus)

Use this code snippet to read this specific value via RS485:

from pymodbus.client.sync import ModbusSerialClient

client = ModbusSerialClient(method='rtu', port='/dev/ttyUSB0', baudrate=9600)
client.connect()

# Read HeatPump Return T16 (Address: 1901)
# Note: Check if your device uses 0-based or 1-based addressing
result = client.read_input_registers(address=1901, count=2, unit=1)

if not result.isError():
    print(f"Raw Value: {result.registers}")
else:
    print("Error reading register")

client.close()

Integration (Home Assistant)

Paste this into your configuration.yaml:

- platform: modbus_controller
  name: "HeatPump Return T16"
  address: 1901
  value_type: S_WORD
  unit_of_measurement: "°C"

Connection Diagram

Here is the standard RS485 wiring for this configuration:

graph TD
    PLC[Host Controller / Home Assistant]
    Device[Geo9]

    PLC -- "A+ (D+)" --> Device
    PLC -- "B- (D-)" --> Device
    PLC -- GND --> Device

💡 Engineer's Insight

Analysis: Return Temperature (T16) of the heat pump's primary loop. Units: °C. Typical range: 25-60°C.

Troubleshooting: Sensor failure, pump issue, or low system load. Could indicate a blocked heat exchanger or refrigerant leak.