Problem of communication between the heater and the TTL<->M-BUS adapter

[casiez]

First, congrats for this project, which is a very nice piece of work!

I'm trying to use the WiFiVitotrol with a Vitodens 200-W WB2B

I successfully managed to build and run the code using an ESP32-U (I did not manage to make the hotspot working but running as a client works well).

Then I connected TTL<->M-BUS adapter on terminals 145 on the heater. Note that the instructions say to connect MB_A and MB_D to the heater, but my adapter has only MB_A and MB_B. It is also unclear to me if the 2 wires to the terminals 145 have to be connected in a specific order.

According to the heater manual p.46 (see link above), I changed the setting A0, from 0 to 1 (Vitotrol 200) and I restarted the heater.

The error led on the heater then gets red and when reading the state of the WiFiVitotrol, it remains in the "Heater is not connected" state, suggesting a problem of communication.

Any suggestion of what to do to troubleshoot this problem?

[dumpfheimer]

MB_D is a typo, fixed it.

Does a red LED blink periodically on your modbus controller?

[casiez]

There are two red LEDs on the modbus controller that do not blink but remain always on.

[dumpfheimer]

Near the center chip there should be 2 more LEDs (RX/TX). If none of them light up occasionally I expect a wiring or heater configuration error. If the outer LEDs are powered if you connect it to the bus the wiring should be fine which would leave the configuration error.

I have no experience with controllers other than WO1C but I needed to enable the remote and then assign a heating circuit.

Also be aware that there might be multiple different modbus (I have one going to the compressor for example)

[casiez]

Thanks! I did not notice the 2 additional LEDs for RX/TX.

It turns out that with my ESP32 board (ESP32-WROOM-32U), I had to change ModbusSerial from Serial1 to Serial2 in configuration.h and I had to set MODBUS_RX to pin 16 and MODBUS_TX to 17. After that, communication seems to work but the WiFiVitotrol remains in the state "Heater is not connected".

In configuration.h, I added the line #define FIND_DEVICE_ID 1 (without that, I keep getting not talking to heater)
Periodically, I get the following message appearing in the console (after running pio device monitor):
OK: 0x1100330A0101F80449EF->0x0011B3100101F811F900FA00FB1162CB

And when querying the state using curl, I get the information below.
The heater still says there is a problem (after changing the setting A0 on the heater, from 0 to 1 (Vitotrol 200)).

Overall, it looks like the communication works. Any suggestion to debug and understand why it cannot get connected to the heater?

Heater is not connected
Communication is prevented
DeviceID found: 0x0
Link state: master requested 4 bytes from F8
Build date: Dec 13 2025 19:02:55

Last com: 265108ms
Last read: 1210ms (cb)
Last message: 1210ms
Last message - last read: 0ms
Last valid message: 1210ms
Last valid broadcast message: 265108ms
Last valid message with response: 1357ms
Last valid message without response: 705066ms
Uptime: 705s

Receive Buffer:
len: 0
ptr: 3ffc431e
content: 


Last message:
len: 10
ptr: 3ffc421f
content: 
11-0-33-a-1-1-f8-4-49-ef-

Last invalid message:
len: 12
ptr: 3ffc4120
content: 
20-0-b3-c-ee-1-10-cb-11-bc-53-12-

Response Buffer:
len: 16
ptr: 3ffc4021
content: 
0-11-b3-10-1-1-f8-11-f9-0-fa-0-fb-11-62-cb-

Data points:


Name: CurrentRoomTemperature
  Value: 0
  Send Value: 0
  Prevent communication: 1
  Has valid value: 0
  Write pending: 0
  Last send: 705066ms ago
  Last set: 705066ms ago
  Periodic send every 30000ms
  Prevent communication after 1800000ms


Name: DesiredRoomTemperature
  Value: 0
  Send Value: 0
  Prevent communication: 0
  Has valid value: 0
  Write pending: 0
  Last send: 705066ms ago
  Last set: 705066ms ago
  Periodic send every 0ms
  Prevent communication after 0ms

[dumpfheimer]

Could you turn off FIND_DEVICE_ID again and send another status page?

It might just need you to set a valid current temperature to not prevent talking to the heater.

You can see the "prevent communication: 0/1" infl for every datapoint. If any of them is on 1 it will not answer to any heater requests which will cause the heater to go into a default heating strategy as if there were no remote connected.

[casiez]

I've turned off FIND_DEVICE_ID and I first tried to set the desired room temperature using curl -d "val=21" -X POST http://xxxx/setDesiredRoomTemperature but the heater remained not connected.

However, after setting the current room temperature, using curl -d "val=18" -X POST http://xxxx/setCurrentRoomTemperature, then the WiFiVitotrol was connected! Wahoo!

I guess both current and desired room temperatures need to be set in order to make it connected.

The heater still displays the blinking red LED indicating there is an error, after changing the setting A0, from 0 to 1, but I'll see that later. Maybe related to that problem, the current room temperature displays 180 when I set it to 18, while the desired room temperature shows 21 when I set it to 21 (see the status below).

Heater is connected
Communication is not prevented
Link state: received message for another device: 20 00 B3 0C
Build date: Dec 13 2025 19:20:30

Last com: 4843ms
Last read: 1612ms (12)
Last message: 1612ms
Last message - last read: 0ms
Last valid message: 1612ms
Last valid broadcast message: 292509ms
Last valid message with response: 4843ms
Last valid message without response: 648538ms
Uptime: 648s

Receive Buffer:
len: 0
ptr: 3ffc431a
content: 


Last message:
len: 11
ptr: 3ffc421b
content: 
11-0-bf-b-1-1-19-57-2d-83-bc-

Last invalid message:
len: 12
ptr: 3ffc411c
content: 
20-0-b3-c-ee-1-10-cb-11-bc-53-12-

Response Buffer:
len: 8
ptr: 3ffc401d
content: 
0-11-80-8-1-1-f9-5c-

Data points:


Name: CurrentRoomTemperature
  Value: 180
  Send Value: b4
  Prevent communication: 0
  Has valid value: 1
  Write pending: 0
  Last send: 27874ms ago
  Last set: 283138ms ago
  Periodic send every 30000ms
  Prevent communication after 1800000ms


Name: DesiredRoomTemperature
  Value: 21
  Send Value: 15
  Prevent communication: 0
  Has valid value: 1
  Write pending: 0
  Last send: 386153ms ago
  Last set: 636427ms ago
  Periodic send every 0ms
  Prevent communication after 0ms

[dumpfheimer]

Great!

The current room temperature is transmitted with 0.1°C precision while the setpoint has 1°C steps. That's the reason for the 180 value.

I'm not sure why your heater is still indicating an error. Do you have multiple heating circuits? Can you confirm the heater is using/receiving the values from the wifi vitotrol using the heaters display?

[MarenB]

Mine also still states an Error frequently although it basically works. I assume some timing issues or similar. I can reset the error, but it will return eventually. Till now I live with it.

Regarding the pin-out: there was (is?) a documentation error here somewhere, I remember I wrote about it, but it wasn't corrected at that time.

[dumpfheimer]

Do you mean this? f828892

[MarenB]

Either this or that:
#14 (reply in thread)

Pin 16/17 are for serial2, if I am not wrong and the default configuration sets serial1 for mbus.

[casiez]

Following further troubleshooting:

• when setting the desired room temperature from my computer, the corresponding value is correctly displayed on the heater display, which is a good sign. Each time I change the value on my computer, I can see the updated value on the display, after some delay (~30s).
• however when setting the current room temperature, the value on the display of the heater remains "- --", suggesting it does not work. I managed to make it working one time by miracle but otherwise it does not work.
• the error code from the heater is bC, corresponding to "problem of communication with the Vitotrol remote control". Even while the heater displays the blinking red LED, setting the desired room temperature works.
• I did all the tests with the configuration for a Vitotrol 200. I quickly tested with the configuration for a Vitotrol 300 but it looks like it is the same.

Any suggestion to debug the problem of setting the current room temperature?

I don't know if it can help, but here are some messages from the console:

TIMEOUT WHILE READING MESSAGE
0
24
1786036
BUFFER:
0 1 0 0 0 0 8 88 11 0 0 8 1 1 8 88 11 0 0 8 1 1 8 88 
OK: 0x1100330A0101F80449EF->0x0011B3100101F811F934FA00FB11A332
OK: 0x11003109010100EE4F->0x0011B10A0101001219D5
OK: 0x1100000801010888->0x001180080101F95C
OK: 0x1100000801010888->0x001180080101F95C
OK: 0x1100000801010888->0x001180080101F95C
OK: 0x1100000801010888->0x001180080101F95C
OK: 0x1100000801010888->0x001180080101F95C
OK: 0x1100000801010888->0x001180080101F95C
OK: 0x1100000801010888->0x0011BF0C01012078AAAAD20A
OK: 0x1100000801010888->0x001180080101F95C
OK: 0x1100000801010888->0x001180080101F95C
OK: 0x1100000801010888->0x001180080101F95C
OK: 0x1100BF0B010119FD8783BC->0x001180080101F95C

[dumpfheimer]

Did you set the DIP switches?

[casiez]

My understanding is that the DIP switches are on the Vitotrol itself. I did not notice DIP switches on the heater board and the heater manual does not mention them. The only setting I changed on the heater is the setting A0, from 0 (no remote) to 1 (Vitotrol 200).

[dumpfheimer]

In the english service manual (https://www.manualslib.com/download/1609271/Viessmann-Vitodens-200-W-Wb2b.html) it says "The DIP switches are located on the PCB in the top part of the casing." on page 101. It does not reference to the Vitotrol 200 which makes me believe they mean in the heater. I could be mistaken though, I only have experience with the vitocal 200s.

[casiez]

I can't find any DIP switches on the heater.

I ran further tests:

• Setting the desired room temperature works like a charm: works all the time
• Setting the current room temperature works from time to time. When it works, the status led on the heater is green and the display on the heater shows the right temperature. At some point it stops working (even when not actively changing the value of the current room temperature), the status led on the heater blinks red, and the display on the heater shows "- --" for the current room temperature. The current room temperature is periodically sent the heater every 30s. I've tried to change the value to 10s but it did not help.