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 Mac, it powered up correctly, but I decided to flash the latest firmware to ensure stability.

Since the flash (and resetting everything), 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?

I'd like to roll back to the prior version I had (with the very basic web tool on the device - but I can't seem to find how to flash these versions as https://adapter.ebusd.eu/v5-c6/firmware.en only lists very recent updates - and at https://adapter.ebusd.eu/v5-c6/firmware_version.html I can't seem to select older versions if I connect the adapter to my Mac.

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]

eBUS wires are connected as before - and blinking. If I remove them, the LEDs are not lit. So I presume the adapter is receiving signal...

[stefbontinckx]

These are the logs without eBUS connected - is my adapter damaged?

IO 9 level 1 is unmet

2026-04-02T16:59:01.331Z W repl: recovered 55 log entries
2026-04-02T16:59:01.331Z I repl: reboot 5 (3), using retained memory for logging
2026-04-02T16:59:01.347Z I memvfs: blocks ^^^^^^^^^^^^^^, 0 valid, 14 free, 0 deleted, 14 total, used x0, damaged x0
2026-04-02T16:59:02.101Z I �[5n0 duty 254
2026-04-02T16:59:02.101Z I 1 duty 254
2026-04-02T16:59:02.101Z I 2 duty 254
2026-04-02T16:59:02.109Z I function 'ledb' installed
2026-04-02T16:59:02.109Z I function 'ledg' installed
2026-04-02T16:59:02.110Z I function 'ledboot' installed
2026-04-02T16:59:02.111Z I function 'leds' installed
2026-04-02T16:59:02.112Z I IO 9 direction set to 03
2026-04-02T16:59:02.112Z I IO 9 pull set to 00
2026-04-02T16:59:02.112Z I IO 9 = 0
2026-04-02T16:59:02.116Z I 0 duty 254
2026-04-02T16:59:02.117Z I 1 duty 254
2026-04-02T16:59:02.117Z I 2 duty 254
2026-04-02T16:59:03.122Z I IO 9 level 1 is unmet
2026-04-02T16:59:03.122Z I 0 duty 254
2026-04-02T16:59:03.123Z I 1 duty 254
2026-04-02T16:59:03.123Z I 2 duty 254
2026-04-02T16:59:04.126Z I IO 9 level 1 is unmet
2026-04-02T16:59:04.127Z I 0 duty 254
2026-04-02T16:59:04.128Z I 1 duty 254
2026-04-02T16:59:04.128Z I 2 duty 254
2026-04-02T16:59:05.131Z I IO 9 level 1 is unmet
2026-04-02T16:59:05.139Z I IO 6 direction set to 01
2026-04-02T16:59:05.139Z I IO 6 pull set to 00
2026-04-02T16:59:05.139Z I IO 6 = 1
2026-04-02T16:59:05.140Z I IO 6 level 1 is unmet
2026-04-02T16:59:05.142Z I var isnew = 0
2026-04-02T16:59:05.145Z I io trigger installed
2026-04-02T16:59:05.146Z I io trigger installed
2026-04-02T16:59:05.147Z I function 'start' installed
2026-04-02T16:59:05.148Z I network trigger installed
2026-04-02T16:59:05.149Z I network trigger installed
2026-04-02T16:59:05.149Z I network trigger installed
2026-04-02T16:59:05.150Z I network trigger installed
2026-04-02T16:59:05.150Z I network trigger installed
2026-04-02T16:59:05.151Z I server trigger installed
2026-04-02T16:59:05.152Z I function 'chkota' installed
2026-04-02T16:59:05.153Z I network trigger installed
2026-04-02T16:59:05.156Z I 0 duty 10
2026-04-02T16:59:05.299Z I using individual IP: 192.168.86.128 / 255.255.255.0, gateway 192.168.86.1
2026-04-02T16:59:05.299Z I sta connecting to 'WaaiFaai'
2026-04-02T16:59:07.869Z I 1 duty 50
2026-04-02T16:59:07.874Z I function 'wpsbtnnew' installed
2026-04-02T16:59:07.877Z I function 'chkethw' installed
2026-04-02T16:59:07.877Z I function 'chketh' installed
2026-04-02T16:59:07.884Z I server started
2026-04-02T16:59:07.908Z I 2 duty 200
2026-04-02T16:59:08.878Z I Ethernet on USR-ES1 not available
2026-04-02T16:59:09.878Z I Ethernet on W5500 module not available
2026-04-02T16:59:10.870Z I 1 duty 0
2026-04-02T16:59:16.909Z I 2 duty 0
2026-04-02T16:59:16.910Z I function 'chkethcfg' installed
2026-04-02T16:59:16.911Z I function 'chkethcfgn' installed
2026-04-02T16:59:16.915Z I function 'enet' installed

[stefbontinckx]

Bus also has 18 volts when reading via multimeter.
Only solution I have left now is ordering a new adapter, which I have done anyway.

[stefbontinckx]

Update after extensive debugging

After extensive debugging, here is a full summary of findings. The root cause remains unclear — hardware damage is possible but not confirmed.

Environment:

• PCB: v1.20.0, ESP32-C3 rev 4
• Firmware tested: 20240809, 20240825, 20241008, 20260317, 20260330
• Connection: WiFi, non-enhanced mode
• ebusd: Home Assistant add-on

Symptoms (consistent across all firmware versions):

• Bus voltage confirmed 18V (Vaillant bus healthy)
• Red LEDs blinking (physical signal present on bus)
• WiFi, web UI, OTA flash all working normally
• eBUS signal: no signal in all firmware versions
• ebus -v always reports detected: no edges
• eBUS r/w counter stays at 0/0 or at most 1/0, never progresses
• Only <00 SYN bytes occasionally appear in history

IO pin observations:

• isio -l 7 → IO 7 level 1 is unmet
• io -iu 7 → IO 7 = 1 (pin reads HIGH when manually initialized)

IO 7 reads LOW via isio but HIGH when manually initialized via io -iu. Unclear if this indicates hardware damage or incorrect initialization.

Firmware-specific finding: uart warning in builds >= 20260104

On firmware 20240825 and 20241008: no UART warning, normal ebus -v output.

On firmware >= 20260104 (after major ESP-IDF UART+JTAG driver migration):

uart: bitrate too slow, unreliable xxx_period values, please try to adjust source_clk
ebus: detected: no edges

This warning appears regardless of ebus -b bitrate deviation value (tested -120 to +120). The source_clk cannot be adjusted via user commands.

This may be a separate regression affecting ESP32-C3 rev 4 + PCB 1.20.0 on newer firmware builds, independent of the no-signal issue.

Questions:

• Is the uart: bitrate too slow / source_clk warning a known issue on ESP32-C3 rev 4 with PCB 1.20.0?
• Could the no edges detection issue be related to firmware/driver rather than hardware damage?

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As I was unable to resolve this issue, I have ordered a new adapter in the meantime. I will report back once it arrives to confirm whether the issue was hardware or firmware related.

Would you have any guidance @john30 ?

[john30]

thats not one of my devices and consequently you can't use my firmware for it

[stefbontinckx]

Hi! Thanks for your reply.
I purchased it on Elecrow, but you were totally right - it's another device.

I had to use https://github.com/danielkucera/esp-arduino-ebus and flash firmware from there.
Incredible how I have missed this. It's working again now.

I've ordered a new one anyway via BerryBase - so I have a backup ready when things go south again.

Very much appreciated your response, it broke me out of my tunnel vision.