Why do some registers return unexpected values when read and written simultaneously?

Registers at addresses like 100, 102, 103, 104, and 105 are holding registers used for both reading and writing. Always read after a write operation to confirm the value was accepted. Avoid simultaneous read and write polling on these addresses.

My write commands are being rejected during the day. What is going on?

The DucoBox Energy firmware enforces a daily limit on write commands. Check register address 31 to see how many writes remain. Reduce the frequency of write operations in your automations to stay within the allowed budget.

I cannot establish a Modbus TCP connection to the DucoBox. What should I check?

Confirm that the connectivity board is installed and powered. Verify the DucoBox IP address and that it is reachable from the gateway's network. Check that no firewall rules are blocking the Modbus TCP port (default is typically 502).

Which DucoBox models are supported by this template?

This template supports the DucoBox Energy Comfort, Comfort Plus, Premium, and Sky models, provided they are equipped with a connectivity board and run firmware supporting API v2.5.

Free Modbus template: DucoBox Energy

Name: DucoBox Energy
Brand: Duco
SKU: e202db48-cb77-4ead-9336-341f083dc435

Template for the DucoBox Energy family of ventilation systems using Modbus TCP (API v2.5). Reads ventilation status, air quality (CO2, RH), temperatures, and flow rates. Allows control of ventilation positions, target temperatures, and mode timing.

Registers (40)

40 read / 9 write

Name	Address	Function	Type	Unit	Access
Ventilation Status box (node 1)	•••	•••	•••		R
Remaining time current ventilation mode box (node 1)	•••	•••	•••	s	R/W
Flow rate vs. Target level box (node 1)	•••	•••	•••	%	R/W
Ventilation position Valve (node 2)	•••	•••	•••		R/W
Ventilation position box (node 1)	•••	•••	•••		R/W
Ventilation position Valve (node 3)	•••	•••	•••		R/W
Ventilation position Valve (node 5)	•••	•••	•••		R/W
Remaining time current ventilation mode Valve (node 2)	•••	•••	•••	s	R
Remaining time current ventilation mode Valve (node 4)	•••	•••	•••	s	R
Remaining time current ventilation mode Valve (node 3)	•••	•••	•••	s	R
Indoor Air quality CO2 Roomsensor (node 5)	•••	•••	•••	%	R
Indoor Air quality CO2 Roomsensor PPM (node 7)	•••	•••	•••	PPM	R
Indoor Air quality RH Box (node 1) Relatieve Luchtvochtigheid qualiteit afzuiging centraal	•••	•••	•••	%	R/W
Indoor Air RH Box (node 1) Relatieve Luchtvochtigheid afzuiging centraal	•••	•••	•••	%	R
Flow rate vs. Target level Valve (node 2)	•••	•••	•••	%	R
Indoor Air quality CO2 Roomsensor (node 6)	•••	•••	•••	%	R
Indoor Air quality CO2 Roomsensor (node 7)	•••	•••	•••	%	R
Indoor Air quality CO2 Roomsensor PPM (node 8)	•••	•••	•••	PPM	R
Indoor Air quality CO2 Roomsensor (node 8)	•••	•••	•••	%	R
Indoor Air quality CO2 Roomsensor PPM (node 6)	•••	•••	•••	PPM	R
Indoor Air quality CO2 Roomsensor PPM (node 5)	•••	•••	•••	PPM	R
Flow rate vs. Target level Valve (node 3)	•••	•••	•••	%	R
Flow rate vs. Target level Valve (node 4)	•••	•••	•••	%	R
Temprature ODA (Outdoor supply)	•••	•••	•••	°C	R
Target supply temperature zone 1	•••	•••	•••	°C	R
Target supply temperature zone 2	•••	•••	•••	°C	R
Target supply temperature zone 3	•••	•••	•••	°C	R
Temprature SUP (Building supply)	•••	•••	•••	°C	R
Temprature ETA (Building Etract)	•••	•••	•••	°C	R
Temprature EHA (Outdoor Etract)	•••	•••	•••	°C	R
Amount of sending commands left for the day	•••	•••	•••	count	R
Target supply temperature zone 4	•••	•••	•••	°C	R/W
Outdoor temprature Sensor	•••	•••	•••	°C	R
Flow rate vs. Target level Valve (node 5)	•••	•••	•••	%	R
Indoor Air quality CO2 Roomsensor (node 9)	•••	•••	•••	%	R
Indoor Air quality CO2 Roomsensor (node 10)	•••	•••	•••	%	R
Indoor Air quality CO2 Roomsensor PPM (node 10)	•••	•••	•••	PPM	R
Indoor Air quality CO2 Roomsensor PPM (node 9)	•••	•••	•••	PPM	R
Remaining time current ventilation mode Valve (node 5)	•••	•••	•••	s	R
Ventilation position Valve (node 4)	•••	•••	•••		R/W

Loading registers…

DucoBox Energy

Overview

Key readings

Available commands

Use cases

Installation

Things to watch for

Registers (40)

Working with Modbus in your projects?

Question about your setup?

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