Nodo OTGW and Vitodens 100

[frazell]

All,

I'm looking for some information on the Nodo OTGW and interaction with a Viesmann Vitodens 100 boiler.

This particular boiler does not return the correct values for boiler max CHW temperature, effectively locking it at 80deg C. The boiler does not provide any interface to be able to set or adjust it.

On another forum one of the members established that using a Nodo OTGW you can intercept the boiler max CHW temperature request (command #57) and send on a new setpoint to the thermostat using the gateway. This was a few years ago and the member found that he had to modify the source code to get this to work as the command did not appear to be forwarded.

I'm mindful that the gateway software has probably moved on a little since 2019 so wondered if sending a modified request to the thermostat is now possible without modifying the source code.

Thanks in advance for any assistance.

Frazell

[hvxl]

Your description is extremely vague. But if you are wondering what has changed in the firmware since 2019, a good place to start looking is the change log. That says there was a change in firmware versions 5.5 and 6.2 for the vitodens: "Init messages that have been marked as unknown are skipped. This allows using the UI=49 command as a work-around for buggy boilers that incorrectly report the current max CH water setpoint as the upper bound (like Viessman Vitodens)". Could that be what you are looking for?

[Dman]

Hi hvxl,

I'm struggling with an older Vitodens W100 boiler (around 10 years old) connected to a Honeywell Evohome thermostat via opentherm and the OTGW in gateway mode between the two of them. I'm trying to set the maximum temperature of the heating water made by the boiler.

As far as I understand, I need to the the UI=49 command, and then I can use the SH=48 to set the maximum setpoint to 48 degree, and use the SR=57:48,00 command to override the maximum CH temperature value coming from the boiler (default 80) to 48.

Am I right? Unfortunately nothing happens when I do these steps. If I set UI=49 I get "UI: 49" in the logs, if I set SH=48 I get "SH: 48" in the logs, and if I set "SR=57:48,00" I get "SR: 57:48/0" in the logs. No errors, but if I set the temperature up on the thermostat, it easily set the CH temperature over the 48 degree. After UI=49 I also tried to do a GW=R to restart the GW.

Please help me out what am I missing?

[Dman]

Sorry, forgot to mention that the OTGW hardware came from Nodo shop, the version is v2.11 running firmware version 6.6.

And here's a part from the logs. The strangest thing is that in this partial log one time (at 9:12:55) overwriting the max ch water setpoint worked, but in the previous and the next minute it did not changed the value.

Code: Select all

09:11:54.031154  T00383100  Read-Data   DHW setpoint: 49.00
09:11:54.212943  BC0383133  Read-Ack    DHW setpoint: 49.20
09:11:54.540367  T00395000  Read-Data   Max CH water setpoint: 80.00
09:11:54.718668  BC0395000  Read-Ack    Max CH water setpoint: 80.00
09:11:55.043367  T900E6400  Write-Data  Maximum relative modulation level: 100.00
09:11:55.346818  B500E6400  Write-Ack   Maximum relative modulation level: 100.00

09:12:55.793898  T00395000  Read-Data   Max CH water setpoint: 80.00
09:12:55.815090  R90393000  Write-Data  Max CH water setpoint: 48.00
09:13:01.597379  BF0390000  Unk-DataId  Max CH water setpoint: 0.00
09:13:01.600018  AC0393000  Read-Ack    Max CH water setpoint: 48.00
09:13:01.618971  T00393000  Read-Data   Max CH water setpoint: 48.00
09:13:01.619617  BC0395000  Read-Ack    Max CH water setpoint: 80.00
09:13:01.621793  T00395000  Read-Data   Max CH water setpoint: 80.00
09:13:01.622541  BC0395000  Read-Ack    Max CH water setpoint: 80.00
09:13:01.628018  T00395000  Read-Data   Max CH water setpoint: 80.00
09:13:01.631039  BC0395000  Read-Ack    Max CH water setpoint: 80.00
09:13:01.952035  T900E6400  Write-Data  Maximum relative modulation level: 100.00
09:13:03.153220  B500E6400  Write-Ack   Maximum relative modulation level: 100.00

09:14:55.242230  T00383100  Read-Data   DHW setpoint: 49.00
09:14:55.441295  BC0383133  Read-Ack    DHW setpoint: 49.20
09:14:55.777816  T00395000  Read-Data   Max CH water setpoint: 80.00
09:14:56.069784  BC0395000  Read-Ack    Max CH water setpoint: 80.00
09:14:56.321655  T900E6400  Write-Data  Maximum relative modulation level: 100.00
09:14:56.581139  B500E6400  Write-Ack   Maximum relative modulation level: 100.00

09:15:55.692824  T00383100  Read-Data   DHW setpoint: 49.00
09:15:55.902366  BC0383133  Read-Ack    DHW setpoint: 49.20
09:15:56.667191  T00395000  Read-Data   Max CH water setpoint: 80.00
09:15:56.675766  BC0395000  Read-Ack    Max CH water setpoint: 80.00
09:15:57.217307  T900E6400  Write-Data  Maximum relative modulation level: 100.00
09:15:57.769817  B500E6400  Write-Ack   Maximum relative modulation level: 100.00

[hvxl]

For some reason your situation is a bit different: Your boiler does not accept a new max CH water setpoint via opentherm (given that it returns Unk-DataId). The suggested fix was for the case where the boiler does accept a new max CH water setpoint, but it would then adjust its bounds.

I won't have time soon to set up a test environment to reproduce your situation, but I suspect the problem may be that the SH command is overridden by the ID57 response from the boiler. Rather than making ID49 unknown, you may need to do that for ID57 instead. I don't even think you need the SR command. The OTGW should already return the value you set with the SH command. You just have to make sure the boiler doesn't get a chance to provide contradicting information.

[Dman]

Thanks for the quick replay!

First of all: as far as I can understand it's impossible to set the maximum CH temperature on the Viessmann boiler if an opentherm thermastat is connected, because Viesmann says the thermostat should know and set the maximum temperature. However on the Honeywell Evohome thermostat there's no way to set the maximum temperature because Honeywell says it's a setting, that should be set on the boiler. So it looks like a stalemate.

Now UI=49 is set. What is the way to undo this? Is there a clear command for UI?

After clearing it I can test setting UI=57 and SH=48 and check what is happening. Or can I use the SR command to override the ID 49? The current value of ID 49 is 80/20 in my system.

[hvxl]

Well, the way for a thermostat to set the maximum CH temperature is to send a Write-Data message for ID57. But your log shows that the boiler responds with Unknown-DataId, indicating that it does not recognize or does not support the message.

To clear the UI=49 command, send a KI=49 command. To clear the SR=57:48,00 command, send a CR=57 command.

A value of 80/20 for ID49 is fine. Those are the bounds. It just means the max CH water setpoint may be set between 20 and 80 degrees. Although it is unclear how to actually set it. But as long as the OTGW can successfully convince the thermostat that the max CH water setpoint is 48, it should not send a control setpoint higher than that.

[Dman]

I cleard the UI=49 and the SR=57:48,00 and set the SH=48 but no luck, the thermostat still send higher values for control setpoint.

And there's one thing in the documentation that's not entirely clear for me at the SH command:
"Setpoint Heating — Set the maximum central heating setpoint. Return control of the central heating setpoint to the thermostat by specifying a temperature of 0. This command is only effective with boilers that support this function."

I interpret the first sentence as the OTGW tells the thermostat what is the maximum value for heating control setpoint, eg. what should be the waters temperature coming out from the boiler. However, the second sentence says with SH=0 OTGW will return the control of the CH setpoint to the thermostat. Return the control of the CH setpoint or the maximum CH setpoint?