eBUS Adapter C6 (ESP32-C3) - "No EBUS Signal" after firmware flash despite blinking LEDs

[stefbontinckx]

Hardware: eBUS Adapter C6 (ESP32-C3, rev 4)
PCB Version: v1.20.0
Current Firmware Build: 20260330 (previously 20260317)
Connection: Ethernet/WiFi to Home Assistant (ebusd add-on)

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Problem Description

After a power outage, my adapter failed to boot. It turned out the USB power supply was no longer providing sufficient power. After connecting the adapter to a PC, it powered up correctly, but I decided to flash the latest firmware to ensure stability.

Since the flash, I am unable to get an eBUS signal in the Web UI, even though the hardware seems to be receiving data physically.

Key Observations

• Physical Connection: The eBUS cabling has not been changed and worked perfectly for a long time.
• Hardware Activity: The LEDs (red) on the adapter are blinking, indicating bus activity. (?)
• Polarity Check: If I swap the eBUS wires, the LEDs stop blinking. This confirms the current wiring/polarity is physically correct and the adapter is receiving power/data from the bus.
• Software Status: The Web UI consistently reports eBUS signal: ❌ no signal.

Troubleshooting Performed

• Multiple factory resets and reboots, and different fimware versions.
• Power-cycled the heat pump (Vaillant) to reset the bus.
• Swapped eBUS polarities (confirmed original was correct as LEDs only blink in one orientation).
• Verified network connectivity (Adapter is reachable via IP, ebusd connects but remains 'inactive', I can connect it to Home Assistant, but that is not the issue. Adapter does not seem to read the EBUS signal anymore).

Historical Context

Everything worked perfectly before the power outage/flash using a very old firmware version (the legacy version with the basic web portal). I had to swap the USB adapter is that one seemed to be suddenly faulty after the short power outage (when I was just pulling the plug - no power network issue etc.)

Question

Why would the Web UI report "No Signal" while the hardware LEDs clearly indicate bus activity? Am I overlooking something by doing the firmware update?

In home assistant I see;
2026-04-02 11:50:58.477 [bus notice] re-opened 192.168.86.128:9999
2026-04-02 11:50:58.485 [device notice] reset, supports info
2026-04-02 11:50:58.492 [device notice] extra info: firmware 1.1[631e].1[631e], jumpers 0x0b

[stefbontinckx]

Duplicate because of Github Error