Connecting a Vaillant VRT350 Thermostat to OpenHAB


This blogpost describes how I connected my Vaillant VRT350 to OpenHAB.

Introduction

The Vaillant VRT350 uses eBUS (energy bus) for communication with the boiler. The Vaillant VRT350 follows the eBUS standard on the physical layer and uses a Valliant specific extensions on the application layer.

eBUS is a bus, meaning multiple devices can be connected to the same bus. Thus it is possible1 to add your own device to the bus (read: wire) running between the boiler and the thermostat. This coupler can then:

  • Read all messages send on the bus.
  • Send messages on the bus.

To control the heating installtion from OpenHAB the following is used:

Hardware

Hardware used

Since my thermostat nor my boiler is near my Raspberry Pi running OpenHAB I’m using the ESERA automation eBUS Coupler Ethernet: ESERA automation eBUS Coupler Ethernet

Configuration

The voltage on the eBUS representing a logical 0/1 varies depending on conditions, including wire length. The ESERA eBUS Coupler Ethernet has a small dial (called Trimmer for signal level in the manual which can be adjusted with the supplied Philips screwdriver. This dial adjusts the coupler to the voltages for your installation. Once connected I adjusted the dial until the “Data” led started blinking. If the led is continuously off/on than the devices only sees a 0/1 on the bus. The Vaillant VRT350 regularly communicates with the boiler so data is more or less continuously going over the bus if the boiler and thermostat are on.

eBUSdeamon frequently reported CRC errors. Those where resolved with some further fine adjustment of the screw.

The ESERA eBUS Coupler Ethernet shipped with a software application for configuration. I had to adjust the Serial data packing conditions to avoid connection timeouts in eBUSdeamon. Note a timer of 1ms is probably causing unnecessary network overhead. WIZ107SR

The ESERA eBUS Coupler Ethernet is well described in the manual.

Software

ebusd installation

From: https://github.com/john30/ebusd-debian/blob/master/README.md 2

Add the GPG key to your trusted apt sources (usually root access required):

wget -qO - https://raw.githubusercontent.com/john30/ebusd-debian/master/ebusd.gpg.key|apt-key add –

Copy the right source list for your architecture (check by executing dpkg –print-architecture) to /etc/apt/sources.list.d/ (replace ARCH with either amd64, armhf or i386):

wget -O /etc/apt/sources.list.d/ebusd.list https://raw.githubusercontent.com/john30/ebusd-debian/master/ebusd-ARCH-default.list

If you prefer the variant without MQTT support, use this command instead (replace ARCH with either amd64, armhf or i386):

wget -O /etc/apt/sources.list.d/ebusd.list https://raw.githubusercontent.com/john30/ebusd-debian/master/ebusd-ARCH-nomqtt.list

After that, you can simply update the package lists via apt-get update(depending on your distribution) and then install with apt-get install ebusd.

Setup ebusd

(My revision of) the VRT350 is not supported at this time (26-Apr-2021) by the ebus config files. (Incomplete) support has been added in this pull request. Hence copy these files. E.g. to: /home/openhabian/ebusd-configuration/ebusd-2.1.x/en/

Remove the i for DesiredTemp and other other desired messages allow the command to be used outside installer mode.

[SW>=114]r;wi,,DesiredTempDay,,,,,"2700",,,D1C,,,
[SW>=114]r;w,,DesiredTempDay,,,,,"2700",,,D1C,,, 2

Configure ebusd to connect to the ESERA eBUS coupler and use the copy of the configuration files by setting the EBUSD_OPTS in /etc/default/ebusd. Here’s an excerpt from my config:
EBUSD_OPTS="-d ebuscoupler.localdomain:5000 --scanconfig -c /home/openhabian/ebusd-configuration/ebusd-2.1.x/en/"

Optionally test ebusd by manually starting ebusd on the command line with the arguments from /etc/default/ebusd. Add -f to run in foreground. Test reading from ebus by executing “ebusctl read DesiredTemp” in a different terminal.

Configure systemd to start ebusd automatically: sudo systemctl enable ebusd

Configure thing(s) in OpenHAB
Install Exec Binding
Add to things:
Thing exec:command:ebusctl_write_DesiredTemp "BeganeGrond:Woonkamer:CV_gewenste_temperatuur_schrijven" [command="ebusctl write -c 350 DesiredTempDay %2$s", interval=0, autorun=true]

Possible future improvements

  • Resolve note: [SW>=114]r;w,,DesiredTemp,,,,,"3C00",,,D1C,,, # Note: Reading and writing is only effective when a specific temperature for today has already been set on the VRT350 today. DesiredTemp is then used rather than DesiredTempLow/DesiredTempDay. How to activate DesiredTemp remotely?
  • Serial data packing conditions > 1ms

Alternatives considered

  • BUS: OpenTHERM → not chosen as this would require exchaning the thermostat.
    • Valliant support.
    • OpenTherm gataway.
  • eBUS interface
    • ESERA eBus Coupler USB
    • eBUS Adapter 3. Pro’s: WiFi, automatic adjustment of eBUS voltages. Cons: PCBs: not available when I was performing my installation.
  • eBUS plugins for OpenHAB
    • eBUS Binding v1 → outdated
    • eBUS 2.0 binding, development continued here → Not included in OpenHAB release. Not as feature rich as ebusd (e.g. grab command).

Recognition

This work is based on numerous others, including: OpenHAB, ebusd, the OpenHAB forum. Thanks!

Notes

  • ebusd wiki describes the ebusd and command line tools in detail:
  • Valliant write command is b5 09 0D. Valliant read command is b5 09 0E. See vaillant_ebus_v0.6.0.pdf.
  • Use grab command in ebusctl to decode data in multiple formats. Read the data first using a hex command and remove the address from the configuration files to avoid “normal” interpretation.
  • To read in hex start ebusd with –enablehex.
  • write >> ebusctl write -c 350 DesiredTemp 19.0
  • read >> ebusctl read DesiredTemp
  • 350 is the name of the thermostat. See xml_config_files.
  • read hex >> ebusctl hex 15b509030d0000

  1. This is not supported by Vailliant. Depending on your local legislation this will void your guarantee. ↩︎

  2. GNU General Public License v3.0 ↩︎