Hello

unfortunately my comment was deleted somehow. Anyway, i´ll try it again.

I have the problem, that I only have a slave device. Its a KS04, the circulation pump of a fire place with water heat exchanger.

There is no Master the device speaks to, but it is possible to buy other devices like controller or sth.

I have the feeling, that the KS04 only sends data if there is a request. But I do not know hoe this request should look like. Any ideas how to find out? Can you maybe show screenshots of the protocol your master uses to talk to your slave?

Thanks in advance!

Hi everyone,

I have a LEDA wood-burning stove with a water heat exchanger controlled by a Ledatronic unit (the old one without wifi), combined with a LEDATHERM KS04 water jacket module. I wanted to get all sensor data into Home Assistant, so I tapped into the internal CAN bus using an AZ-Delivery D1 Mini and an MCP2515 CAN module (125 kbps, 16 MHz crystal) + an RJ12 Jack.

Hardware wiring (D1 Mini ↔ MCP2515):

MCP2515 –> D1 Mini
SCK –> D5 (GPIO14)
SO/MISO –> D6 (GPIO12)
SI/MOSI –> D7 (GPIO13)
CS –> D8 (GPIO15)
INT –> D2 (GPIO4)
VCC –> 3.3V
GND –> GND

Instead of soldering directly to the Ledatronic PCB, I used an RJ12 splitter (Y-adapter) on one of the existing RJ12 bus cables between the Ledatronic modules. This is completely non-invasive — no board modifications, no soldering, and fully reversible.

The RJ12 connector on the Ledatronic bus carries (among others) CAN-H and CAN-L. I wired those two lines plus GND from the RJ12 splitter directly to the MCP2515 module.

Decoded CAN frames:

ID 0x281 — Main stove frame (~every 6s):
Bytes 0+1: Combustion chamber temperature (°C), 16-bit Little Endian
Byte 2: Air damper actual position (%)
Byte 3: Air damper target position (%)
Byte 4: Operating state

Code State
0x00 Standby
0x01 Door closed
0x02 Cold start / Kindling
0x03 High heating
0x04 Normal heating
0x07 Embers
0x08 Embers part-load
0x09 Part-load operation
0x61 Heating fault
0xE2 Door open

ID 0x288 — LEDATHERM KS04 water jacket (~every 6s):
Byte 1: Buffer temperature top (°C)
Byte 2: Buffer temperature bottom (°C)
Byte 3: Water jacket temperature (°C)
Byte 4: Pump power (%)

ID 0x28A — Sensor data (multiple subtypes per second):
Subtype 0x00: x = draught pressure (Pa), x = flue gas temperature (°C)
Subtype 0x01: x = ventilation active flag

ESPHome YAML (full config below ### signs — just add your secrets):

### YAML START ###

substitutions:
name: kachelofen
friendly_name: Kachelofen

esphome:
name: ${name}
friendly_name: ${friendly_name}
min_version: 2023.6.0

esp8266:
board: d1_mini

# Logging auf DEBUG damit alle CAN-Frames in der Konsole erscheinen
logger:
level: DEBUG
baud_rate: 115200

# Home Assistant API
api:
encryption:
key: !secret api_key

# OTA-Updates
ota:
platform: esphome
password: !secret ota_password

# WLAN
wifi:
ssid: !secret wifi_ssid
password: !secret wifi_password
min_auth_mode: WPA2

captive_portal:

# Optionaler Webserver (Logs auch im Browser erreichbar)
web_server:
port: 80

# SPI-Bus – Hardware-Pins des D1 Mini
spi:
clk_pin: GPIO14 # D5
miso_pin: GPIO12 # D6
mosi_pin: GPIO13 # D7

canbus:
– platform: mcp2515
id: can_bus
cs_pin: D8
can_id: 0x000
bit_rate: 125kbps
on_frame:

# =========================================================
# ID 0x281 – Ofen-Hauptframe (alle ~6s)
# Byte 0+1: Feuerraumtemperatur °C, 16-bit Little Endian
# Byte 2: Luftklappe Ist-Position (%)
# Byte 3: Luftklappe Soll-Position (%)
# Byte 4: Betriebszustand (Status-Codes s.u.)
# Byte 5-7: Konstant (weitere Aktoren, falls vorhanden)
# =========================================================
– can_id: 0x281
then:
– lambda: |-
// — Feuerraumtemperatur (16-bit Little Endian) —
float feuerraum = (float)((uint16_t)x[0] | ((uint16_t)x[1] << 8));
id(sensor_ofen_feuerraum_temp).publish_state(feuerraum);

// — Luftklappe —
id(sensor_ofen_klappe_ist).publish_state((float)x[2]);
id(sensor_ofen_klappe_soll).publish_state((float)x[3]);

// — Betriebszustand —
uint8_t status = x[4];
switch (status) {
case 0x00:
id(sensor_ofen_betriebszustand).publish_state("Bereit");
break;
case 0x01:
id(sensor_ofen_betriebszustand).publish_state("Tür wurde geschlossen");
break;
case 0x02:
id(sensor_ofen_betriebszustand).publish_state("Anheizen Kaltstart");
break;
case 0x03:
id(sensor_ofen_betriebszustand).publish_state("Heizbetrieb Hochheizen");
break;
case 0x04:
id(sensor_ofen_betriebszustand).publish_state("Heizbetrieb");
break;
case 0x07:
id(sensor_ofen_betriebszustand).publish_state("Grundglut");
break;
case 0x08:
id(sensor_ofen_betriebszustand).publish_state("Grundglut Teillast");
break;
case 0x09:
id(sensor_ofen_betriebszustand).publish_state("Teillastbetrieb");
break;
case 0x61:
id(sensor_ofen_betriebszustand).publish_state("Heizfehler");
break;
case 0xE2:
id(sensor_ofen_betriebszustand).publish_state("Tür geöffnet");
break;
default: {
char buf[20];
snprintf(buf, sizeof(buf), "Unbekannt (0x%02X)", status);
id(sensor_ofen_betriebszustand).publish_state(buf);
break;
}
}

# =========================================================
# ID 0x288 – LEDATHERM KS04 / Wassertasche (alle ~6s)
# Byte-Zählung im Forum 1-basiert → hier 0-basiert:
# x[1] = Speichertemperatur oben (°C)
# x[2] = Speichertemperatur unten (°C)
# x[3] = Temperatur Wassertasche (°C)
# x[4] = Pumpenleistung (%)
# =========================================================
– can_id: 0x288
then:
– lambda: |-
id(sensor_ofen_speicher_oben).publish_state((float)x[1]);
id(sensor_ofen_speicher_unten).publish_state((float)x[2]);
id(sensor_ofen_wassertasche).publish_state((float)x[3]);
id(sensor_ofen_pumpe).publish_state((float)x[4]);

# =========================================================
# ID 0x28A – Sensor-Daten (Subtyp via x[0])
#
# Subtyp 0x00:
# x[1] = Zugdruck (Pa)
# x[3] = Abgastemperatur (°C)
#
# =========================================================
– can_id: 0x28A
then:
– lambda: |-
if (x[0] == 0x00) {
float pressure = x[1]*0.1f + (x[2]==0x81 ? 25.5f : 0);
id(sensor_ofen_zugdruck).publish_state(pressure);
id(sensor_ofen_abgas_temp).publish_state((float)x[3]);
} else if (x[0] == 0x01) {
bool vent = (x[5] == 0x01);
id(binary_sensor_ofen_lueftung_aktiv).publish_state(vent);
}

# =========================================================
# BINARY SENSOREN
# =========================================================
binary_sensor:
– platform: template
id: binary_sensor_ofen_lueftung_aktiv
name: "Lüftung aktiv"

# =========================================================
# SENSOREN
# =========================================================
sensor:

# — Ofen (0x281) —
– platform: template
id: sensor_ofen_feuerraum_temp
name: "Brennraumtemperatur"
unit_of_measurement: "°C"
device_class: temperature
state_class: measurement
icon: "mdi:fire"
accuracy_decimals: 0
filters:
– delta: 0.5

– platform: template
id: sensor_ofen_klappe_ist
name: "Luftklappe Ist-Position"
unit_of_measurement: "%"
state_class: measurement
icon: "mdi:valve"
accuracy_decimals: 0
filters:
– delta: 0.5

– platform: template
id: sensor_ofen_klappe_soll
name: "Luftklappe Soll-Position"
unit_of_measurement: "%"
state_class: measurement
icon: "mdi:valve"
accuracy_decimals: 0
filters:
– delta: 0.5

# — Speicher & Wassertasche (0x288) —
– platform: template
id: sensor_ofen_speicher_oben
name: "Speichertemperatur oben"
unit_of_measurement: "°C"
device_class: temperature
state_class: measurement
icon: "mdi:thermometer-chevron-up"
accuracy_decimals: 0
filters:
– delta: 0.5

– platform: template
id: sensor_ofen_speicher_unten
name: "Speichertemperatur unten"
unit_of_measurement: "°C"
device_class: temperature
state_class: measurement
icon: "mdi:thermometer-chevron-down"
accuracy_decimals: 0
filters:
– delta: 0.5

– platform: template
id: sensor_ofen_wassertasche
name: "Wassertasche Temperatur"
unit_of_measurement: "°C"
device_class: temperature
state_class: measurement
icon: "mdi:thermometer-water"
accuracy_decimals: 0
filters:
– delta: 0.5

– platform: template
id: sensor_ofen_pumpe
name: "Pumpenleistung"
unit_of_measurement: "%"
state_class: measurement
icon: "mdi:pump"
accuracy_decimals: 0
filters:
– delta: 0.5

# — Zugdruck & Abgas (0x28A) —
– platform: template
id: sensor_ofen_zugdruck
name: "Zugdruck"
unit_of_measurement: "Pa"
device_class: pressure
state_class: measurement
icon: "mdi:gauge"
accuracy_decimals: 0
filters:
– delta: 0.5

– platform: template
id: sensor_ofen_abgas_temp
name: "Abgastemperatur"
unit_of_measurement: "°C"
device_class: temperature
state_class: measurement
icon: "mdi:smoke"
accuracy_decimals: 0
filters:
– delta: 0.5

# =========================================================
# TEXT SENSOREN
# =========================================================
text_sensor:
– platform: template
id: sensor_ofen_betriebszustand
name: "Betriebszustand"
icon: "mdi:fire-circle"

### YAML – END ###

Notes:
All sensor IDs use the sensor_ofen_ prefix to keep things tidy in HA.

filters: – delta: 0.5 on every sensor prevents HA from being flooded with updates — values are only published when they actually change. The 0x28A frame arrives several times per second, so this filter makes a real difference.

Status codes were originally documented by Wohnmaschine and Morpheus on the FHEM/Homematic community forums back in 2020 — big credit to them for the groundwork.

Happy to answer questions if you have the same setup.
Feel free to adjust the wording or add your name/handle before posting!