KNX App sends lighting commands with High priority instead of Low (blocking Schneider/Merten actuators)

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Hi everyone,

I wanted to share a technical issue (and solution) I ran into while setting up a KNX integration with Homey Pro and a Schneider SpaceLogic / Merten system. I hope this can be addressed in a future update of the official Homey KNX app!

The Problem

When controlling lights via the Homey KNX app, Homey can read status/temperature values from the bus fine, but light actuators fail to toggle.

After diving deep into the ETS Group Monitor, I noticed that Homey injects all GroupValue_Write telegrams onto the KNX bus using Telegram Priority: HIGH (High).

When standard physical KNX push-buttons or ETS send commands, they use Telegram Priority: LOW (Low).

Why this causes lights not to turn on/off

In the KNX specification:

  • Low / Normal Priority: Used for standard, manual lighting and blind controls.

  • High Priority: Reserved for forced control, safety overrides, or higher-level logic.

Certain strict KNX actuators (such as the Schneider Electric SpaceLogic SA1 Switch/Blind Master line, e.g., MTN6705-0008) enforce a strict priority filter on standard switching input objects

When Homey sends a switch command with Priority: High to a standard light output:

  1. The actuator receives the packet on the bus.

  2. It triggers its status-engine (and sends a status feedback object back onto the bus).

  3. Crucially: It ignores the physical relay trigger because the incoming telegram carries High priority on an input expecting Low priority.

ETS Bus Log Comparison

Here is the direct comparison from the ETS Group Monitor on the exact same Group Address (1/1/23):

  • Command sent via ETS (WORKS - Relay clicks):

    from bus | Low | 1.0.255 | 1/1/23 | GroupValue_Write | $01 | On (Feedback responds with $01 | On)

  • Command sent via Homey (FAILS - No relay click):

    to bus | High | 1.0.254 | 1/1/23 | GroupValue_Write | $01 | On (Actuator ignores the command and immediately responds with its unchanged status $00 | Off)

Suggested Fix for Athom / Developers

According to KNX standard practices, routine user commands (turning a light on/off, dimming, moving blinds) should be dispatched with Priority.LOW (or Priority.NORMAL).

It would be fantastic if:

  1. Athom updates the default outgoing priority for lighting/appliance drivers in the KNX app to LOW.

  2. Or provides an option under the Advanced Device Settings to select the Telegram Priority (Low, Normal, High).

Has anyone else encountered this with Schneider, Merten, or ABB actuators? Hope this detailed trace helps the Athom dev team resolve this!