HT3 Write Commands questions

[ooassel]

Feature Request: Enable HT3 Write Commands in EMS-ESP Firmware

Summary
Many users with Junkers/Worcester boilers that use the HT3 (Heatronic 3) protocol would benefit from support for write commands—such as setting room temperature, changing operating modes, and updating the system clock—directly via EMS-ESP. Currently, HT3 is only supported in read-only mode, limiting home automation scenarios and remote control capabilities.

Use Case
On HT3-based systems (e.g., Junkers CW400/RC3*, Moduline 3000/1010H, CW400, Sense II), users can already read sensor values and system status through EMS-ESP. However, there is no way to:
-Adjust target room temperature
-Switch between operating modes (comfort/eco/auto)
-Manually update date/time without relying on NTP gateway workarounds

Enabling HT3 write commands would allow full two-way control of HT3 boilers through REST, MQTT, or the web UI—bringing feature parity with EMS/EMS+ implementations.

Proposal

1. Implement the HT3 write telegram formats used by the Junkers service interface (Heatronic 3) in the EMS-ESP core library.
2. Expose new API endpoints (REST and MQTT) under the existing /api/.../command and ems-esp/.../command topics for HT3 devices.
3. Add configuration options to enable/disable HT3 write support and required authentication tokens.
4. Update documentation and examples for HT3 write commands.

Benefits

• Full remote control of HT3-based boilers via EMS-ESP
• Unified API for EMS, EMS+ and HT3 devices
• Reduce reliance on proprietary service tools for common tasks
• Improve integration with Home Assistant, openHAB, ioBroker, and other platforms

Thank you for considering this feature!

[proddy]

EMS-ESP supports write commands for Heatronic systems just like the EMS protocols. You can see the pencil icon in the screenshot you sent. If you're getting errors then something else is wrong. We would need to see the System Info details and the log when a write action fails.

[ooassel]

Thank you for the clarification. I was misled by my earlier assumption that HT3 is read-only. It appears that the length or format of the payload was or is incorrect. I simply retained the syntax given during input and changed the data, but a completely different syntax is required. This is not apparent at all in Home Assistant. Perhaps this could be changed:

[proddy]

The length of the string must be 23 chars in the format dd.mm.yyyy-hh:mm:ss-D-S where D=Day of week and S is either 0 or 1 for summertime. It looks like its working from the WebUI and not MQTT?

Other than the datetime is there anything else not working, because I want to change the the title of this issue to reflect the actual issue you're experiencing

[ooassel]

Regarding the date/time, it is not possible to simply change the -predefined- value (dd.mm.yyyy hh:mm); instead, the day of the week and daylight saving time must be added manually. It would be helpful if the correct syntax were specified in the input field, -or- things like the day of the week/daylight saving time could simply be omitted. (is day 0 Sunday or Monday?).

Other write communication occurs without error messages, but is only partially implemented. Example: circulation—it appears that the correct bits are not being set.

MQTT should work correctly; so far, it behaves the same way, or rather, the same problems occur in HA.
I am focusing on the local level first, as I hope to initially obtain time-critical values such as “heating circuit flow rate” correctly.

[proddy]

The manual date/time is doing precisely what is described so I don't see any fault in the software at this point. We could omit the day number and summer time, but this is the protocol from HT3 so we're bound to that.

For the circulation, I also don't see anything wrong. Please open a new issue for this, with a reproducible use case, logs and the system info as described in https://docs.emsesp.org/Support/ so we can trace the cause of the error.

Moving to a discussion.

[ooassel]

The date/time displayed in ems-esp already omits the day number and daylight saving time, as shown in my screenshot.
I have not changed the value; it is displayed in the format dd.mm.yyyy hh:mm.
If the HT3 protocol has a different format, this should also be displayed accordingly.
Currently, in EMS-ESP, there is no way to identify which day of the week or whether daylight saving time is stored.

Circulation is just one example of what appears to be working, but unfortunately has no effect on the heater.
I will create a new thread on this topic.