Heat Pump.Mar.Bas Modbus Register 128: Hot Water Tank Temperature

Technical Definition

The register Hot Water Tank Temperature at address 128 is used to monitor hot water tank Temperature on the Heat Pump.Mar.Bas.

• 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 Hot Water Tank Temperature (Address: 128)
# Note: Check if your device uses 0-based or 1-based addressing
result = client.read_input_registers(address=128, 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: "Hot Water Tank Temperature"
  address: 128
  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[Heat Pump.Mar.Bas]

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

💡 Engineer's Insight

Analysis: Indicates the Temperature of the hot water storage tank in degrees Celsius. Essential for domestic hot water availability.

Troubleshooting: Zero might mean the tank heating element failed, sensor malfunction, or the tank is empty/not filling.