Heatpump Modbus Register 138: Water Flow

Technical Definition

The register Water Flow at address 138 is used to monitor water flow on the heatpump.

• Protocol: Modbus RTU
• Data Type: U WORD
• Unit: m3/H
• 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 Water Flow (Address: 138)
# Note: Check if your device uses 0-based or 1-based addressing
result = client.read_input_registers(address=138, 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: "Water Flow"
  address: 138
  value_type: U_WORD
  unit_of_measurement: "m3/H"

Connection Diagram

Here is the standard RS485 wiring for this configuration:

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

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

💡 Engineer's Insight

Analysis: Flow rate of water within the heating/cooling circuit, measured in Liters per minute (LPM) or similar.

Troubleshooting: Zero indicates pump failure, blockage, or valve closure. Essential for heat transfer.