I am not getting any response from the GTW08 on the Modbus bus. What should I check?

Verify that the RS-485 wiring polarity (A and B) is correct and that the slave address configured on the GTW08 matches the address set in the ModbusCloud template. Also confirm the baud rate is set to 9600 with 8 data bits, no parity, and 1 stop bit.

Which Baxi and De Dietrich models are compatible with the GTW08?

Compatibility depends on the GTW08 firmware version and the specific HVAC model. Consult the GTW08 manufacturer documentation for the current list of supported units. Updating the GTW08 firmware may add support for newer models.

Can I control both heating and cooling simultaneously from ModbusCloud?

The template provides separate on/off controls for heating and cooling. Whether simultaneous operation is possible depends on the connected HVAC unit and its configuration. In most setups, the season mode register determines which mode is active.

Temperature values appear incorrect or scaled wrong. How do I fix this?

Check the GTW08 documentation for the expected register data format and scaling factor. The template uses default scaling as documented by the gateway manufacturer. If the firmware version uses a different scale, adjust the register multiplier in the ModbusCloud template settings.

How it works Pricing

Try the demo Shop

Dutch company. EU-hosted. GDPR-compliant.

Product

Gateway
Shop
Diagnostics
How it works
Pricing
Try the demo

Company

About us
Knowledge Base
Templates
Contact

Legal

Privacy policy
Terms and conditions
Data Processing Agreement
Cookies
Impressum

Free Modbus template: GTW08 Gateway | ModbusCloud

///GTW08 Gateway

Modbus RTU

GTW08 Gateway

Name: GTW08 Gateway
Brand: GTW08
SKU: 6242ed38-f747-4fe0-b6c9-bcc055765249

GTW08

Controls Baxi and Dietrich A/C systems via Modbus gateway

Overview

The GTW08 is a Modbus RTU gateway that enables monitoring and control of Baxi and De Dietrich heating and cooling systems. This template reads temperature values, operating status, and season mode, while providing control over setpoints, on/off states, and heating modes.

Key readings

On/Off Heating
On/Off Cooling
On/Off ACS
Setpoint
Season Mode
Outdoor Temp
Ambient Temp

Heating Mode

Available commands

On/Off Heating
On/Off Cooling
Setpoint
Heating Mode

Use cases

Monitor ambient and outdoor temperatures on a live dashboard to verify heating system performance.
Remotely switch heating or cooling on and off for Baxi or De Dietrich units without a site visit.
Adjust the temperature setpoint from the cloud when a building occupant requests a comfort change.
Create an alert when outdoor temperature drops below a threshold to anticipate increased heating demand.
Track season mode changes over time to optimize energy usage across heating and cooling seasons.
Verify domestic hot water (ACS) status to ensure availability for end users.

Installation

1Connect the GTW08 gateway to the Baxi or De Dietrich HVAC unit following the GTW08 manufacturer wiring instructions.
2Wire the RS-485 A and B terminals of the GTW08 to the corresponding terminals on the ModbusCloud gateway (MCG or MLP series), observing correct polarity.
3Set the Modbus RTU slave address on the GTW08 and ensure the baud rate is configured to 9600, 8N1.
4Power on both the GTW08 and the ModbusCloud gateway, then verify the RS-485 bus connection with a quick register read test.
5Import the GTW08 template in the ModbusCloud platform and assign it to the correct gateway and slave address.
6Confirm that temperature readings and on/off statuses appear correctly on the ModbusCloud dashboard before leaving the site.

Things to watch for

I am not getting any response from the GTW08 on the Modbus bus. What should I check?: Verify that the RS-485 wiring polarity (A and B) is correct and that the slave address configured on the GTW08 matches the address set in the ModbusCloud template. Also confirm the baud rate is set to 9600 with 8 data bits, no parity, and 1 stop bit.
Which Baxi and De Dietrich models are compatible with the GTW08?: Compatibility depends on the GTW08 firmware version and the specific HVAC model. Consult the GTW08 manufacturer documentation for the current list of supported units. Updating the GTW08 firmware may add support for newer models.
Can I control both heating and cooling simultaneously from ModbusCloud?: The template provides separate on/off controls for heating and cooling. Whether simultaneous operation is possible depends on the connected HVAC unit and its configuration. In most setups, the season mode register determines which mode is active.
Temperature values appear incorrect or scaled wrong. How do I fix this?: Check the GTW08 documentation for the expected register data format and scaling factor. The template uses default scaling as documented by the gateway manufacturer. If the firmware version uses a different scale, adjust the register multiplier in the ModbusCloud template settings.

Registers (8)

8 read / 4 write

Name	Address	Function	Type	Unit	Access
On_Off Heating	500	FC04	uint16		R/W
On_Off Cooling	502	FC04	uint16		R/W
On_Off ACS	501	FC04	uint16		R
Setpoint	664	FC04	uint16	°C	R/W
Season Mode	385	FC04	uint16		R
Outdoor Temp	384	FC04	uint16	°C	R
Heating Mode	649	FC04	uint16		R/W
Ambient Temp Temperatura Ambiente media por termostato	1104	FC03	uint16	°C	R

Working with Modbus in your projects?

ModbusCloud is the hardware-plus-software platform that installers use to monitor, visualise and control Modbus devices from one portal. This template is one of hundreds you can use right away.

See the live demo How it works

More RTU templates

Alnor HRU-P

Alnor Systemy Wentylacji Sp. z o. o.

Modbus RTU

Controls Alnor HRU-P heat recovery ventilation units via Modbus RTU.

49 registers7

Alnor HRU

Alnor Systemy Wentylacji Sp. z o. o.

Modbus RTU

Controls and monitors Alnor heat recovery ventilation units via Modbus RTU.

29 registers13

Wattsonic - Schmachtl Sun Energy Box

Wattsonic

Modbus RTU

Monitors Schmachtl Wattsonic hybrid inverter via Modbus RTU

92 registers72

Heidelberg Wallbox Energy Control

AMPERFIED GmbH

Modbus RTU

Controls and monitors Heidelberg Wallbox Energy Control EV charger via Modbus RTU.

22 registers67

connecdoor.controller

connecdoor

Modbus RTU

Controls and monitors smart door access points via RS485

0 registers53

Belimo Air-Water Actuator Modbus RTU

Belimo

Modbus RTU

Controls communicative damper and valve actuators via Modbus RTU.

20 registers46

Specifications

Protocol: Modbus RTU
Brand: GTW08
Registers: 8
Compatible models: GTW08
Last updated: 2 April 2026

Want to professionalise your projects?

EU-hosted

Data in the Netherlands and Germany

Open standard

Based on Modbus RTU/TCP

Free to browse

No account or payment required

European company

Based in the Netherlands