Nest Thermostat / Opentherm faulty after OTGW connect

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Nest Thermostat / Opentherm faulty after OTGW connect

Postby linezer0 » Wed Oct 23, 2019 8:45 pm

Hello guys,

i have bought an Opentherm Gateway from Nodo-Shop to connect to my Viessmann Vitodens 111-W. My boiler was running before that with a Google Nest 3rd Gen. thermostat without any problems. Two days ago i have connected the OTGW between the boiler and the Heatlink of the thermostat and tried the connection via serial and then through a NodeMCU. Everything was actually running good, besides the fact that i could not change some parameters, as these were apparently not supported by the Nest thermostat.

So i left the OTmonitor yesterday afternoon running on my Raspberry Pi. Today in the morning i had an error message on the boiler (F:R9) and no connectivity to my Nest thermostat (Error H73). Now i have tried everything to get at least the Nest Thermostat running as it was before (reset heatlink and thermostat), but i get constant error messages from the thermostat telling me that my equipment can not be controlled through it. The heatlink is currently blinking. I am worried that the OTGW has fried the PCB of my boiler or something in the heatlink.

I would be glad if you have any ideas or advices.

Adrian
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Re: Nest Thermostat / Opentherm faulty after OTGW connect

Postby hvxl » Fri Oct 25, 2019 9:44 am

It is pretty much impossible for the gateway to damage the boiler. The part of the circuitry in the gateway that the boiler is connected to is powered by the boiler itself and is completely galvanically isolated from the rest of the gateway circuitry. The worst it can do is to short out the connection. But that is an allowed state in the Opentherm protocol. So any Opentherm boiler should be able to survive that.

If problems persist, I would suggest to power off the boiler for some amount of time (several minutes) and then try again. If you just connect the gateway to the boiler (without a thermostat) you should already see messages go back and forth.
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Re: Nest Thermostat / Opentherm faulty after OTGW connect

Postby linezer0 » Sun Oct 27, 2019 1:08 am

Thank you for the quick reply and explanation. I really appreciate your work and was very glad i found the OTGW, as it was very easy to implement with my limited knowledge in electronics.

Regarding the issue, i have reset the Nest Heatlink and that seems to be running, but i did not manage to reconnect it to the thermostat at first (error H71). I am currently not at home, but i will try again in the next days.

Could it be possible, that the problems i had have been caused by the fact that i switched from Gateway to Monitoring in the OTmonitor, while it was running or the fact that the OTmonitor is constantly requesting infos about the state of the boiler, which the boiler can not process properly (sorry if the question is stupid). I have thought about setting PS=1, as i was worried seeing how many parameters are logged in OTmonitor, but i think that would limit the possibilities of the Gateway.

Greetings Adrian
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Re: Nest Thermostat / Opentherm faulty after OTGW connect

Postby hvxl » Sun Oct 27, 2019 10:33 am

The gateway doesn't request info from the boiler any more frequently than the thermostat does. In fact, most of the time it just forwards the requests from the thermostat to the boiler. In the few cases where it does request other information, it does so by replacing a request from the thermostat that it has already learnt the boiler doesn't support. So the message frequency stays the same.

The Opentherm specification even states that a message must be sent at least once every 1.15 seconds, with a minimum gap of 100ms since the last response. So the boiler should be designed to handle several messages per second. If anything, the gateway will decrease the number of messages, because in gateway mode it causes a slight delay in the message exchange. It first has to receive the message from the thermostat, which it then retransmits. This delays the message by around 34ms. The same happens with the response.

Changing to summary mode (PS=1) does not influence the number of Opentherm messages exchanged between the thermostat and the boiler. It only affects the amount of data reported over the serial interface.

A command to switch from gateway mode to monitor mode is postponed by the gateway if an Opentherm message is currently in progress. So this shouldn't cause any corrupted communication.

What actually happened is unclear. If you have a log of the event, that could provide some clues. Otherwise make sure you collect some logs next time you try.

One possible scenario is that maybe the reference voltage is too close to the switching point. After running for a while, things warm up, which could move the levels enough for the communication to stop. I don't know how your boiler would react to such a situation.

To check that your reference voltage isn't near the edge, connect the thermostat to the gateway and change the reference voltage up and down until you see no messages from the thermostat anymore. There should be several VR settings that work. Finally set the voltage reference in the middle of the range that works.

For example: If you see no messages with VR=1, you do with VR=2 to VR=6, and they stop again when you increase VR to 7, then set VR to 4.
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Re: Nest Thermostat / Opentherm faulty after OTGW connect

Postby linezer0 » Sun Oct 27, 2019 2:28 pm

Wow...thank you very much for the detailed explanation! It shows how much work and know-how you have invested in designing the gateway. I was a bit worried to connect the gateway again to the boiler, but after reading this am going to do this without worries. I will make sure to log everything next time and will get back in case the issue might occur again.
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Re: Nest Thermostat / Opentherm faulty after OTGW connect

Postby linezer0 » Fri Dec 20, 2019 11:31 am

Hello, i tried again connecting the OTGW with the Nest, but am constantly getting the H73 error message (no compatible Opentherm device found). I have already tried resetting the heatlink, setting OTGW from gateway to monitor, setting power supply from 24V to 20V and also changing the voltage in OTGW. Nothing seems to work. Will try again to connect without the NodeMCU through FTDI, to see if that still works. I am worried that something is faulty now, as it worked before with the same setup. Any ideas or advices are welcome.
I have found the logs, but can not upload them here, so i will attach only a part of it.

Old (before it stopped working)

22:30:51.421581 Command: PR=A
22:30:51.506622 PR: A=OpenTherm Gateway 4.2.5
22:30:51.511865 Command: SC=22:30/1
22:30:51.517323 Command: SR=21:10,21
22:30:51.522345 Command: SR=22:7,227
22:30:51.570592 T80310000 Read-Data Max CH setpoint boundaries: 0 0
22:30:51.617047 SC: 22:30/1
22:30:51.726437 SR: 21:10/21
22:30:51.731567 SR: 22:7/227
22:30:51.827947 B40313C14 Read-Ack Max CH setpoint boundaries: 60 20
22:30:52.028266 T80380000 Read-Data DHW setpoint: 0.00
22:30:52.229475 B40382E00 Read-Ack DHW setpoint: 46.00
22:30:52.424370 T00390000 Read-Data Max CH water setpoint: 0.00
22:30:52.736826 BC0393C00 Read-Ack Max CH water setpoint: 60.00
22:30:52.937881 T00710000 Read-Data Unsuccessful burner starts: 0
22:30:53.242645 BC0710003 Read-Ack Unsuccessful burner starts: 3
22:30:53.440655 T00720000 Read-Data Flame signal too low count: 0
22:30:53.750195 B40720001 Read-Ack Flame signal too low count: 1
22:30:53.957934 T00740000 Read-Data Burner starts: 0
22:30:54.258658 BC074212D Read-Ack Burner starts: 8493
22:30:54.543351 T00780000 Read-Data Burner operation hours: 0
22:30:54.742779 B407803DF Read-Ack Burner operation hours: 991


New (today trying to connect)

09:36:04.460072 00000000
09:36:05.413639 R00000000 Read-Data Status: 00000000 00000000
09:36:06.414779 R00000000 Read-Data Status: 00000000 00000000
09:36:07.409916 R00000000 Read-Data Status: 00000000 00000000
09:36:08.428529 R00000000 Read-Data Status: 00000000 00000000
09:36:09.408111 R00000000 Read-Data Status: 00000000 00000000
09:36:10.398213 R00000000 Read-Data Status: 00000000 00000000
09:36:11.414085 R00000000 Read-Data Status: 00000000 00000000
09:36:12.438237 R00000000 Read-Data Status: 00000000 00000000
09:36:13.398793 R00000000 Read-Data Status: 00000000 00000000
09:36:14.523316 R00000000 Read-Data Status: 00000000 00000000
09:36:15.552194 R00000000 Read-Data Status: 00000000 00000000
09:36:17.390137 R00000000 Read-Data Status: 00000000 00000000
09:36:17.499770 R00000000 Read-Data Status: 00000000 00000000
09:36:18.369225 R00000000 Read-Data Status: 00000000 00000000
09:36:19.439012 R00000000 Read-Data Status: 00000000 00000000
09:36:20.421346 R00000000 Read-Data Status: 00000000 00000000
09:36:20.823865 Command: PR=M
09:36:20.978731 PR: M=G
09:36:21.405400 R00000000 Read-Data Status: 00000000 00000000
09:36:22.390075 R00000000 Read-Data Status: 00000000 00000000
09:36:22.970158 Command: GW=0
09:36:23.086702 GW: 0
09:37:04.218062 Command: PR=M
09:37:04.521086 R: M=M
09:37:05.191754 Command: PR=V
09:37:05.199950 Command: PR=T
09:37:05.210633 Command: PR=S
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Re: Nest Thermostat / Opentherm faulty after OTGW connect

Postby linezer0 » Tue Dec 31, 2019 2:11 pm

Unfortunately i did not get the chance to try out the FTDI connection again, but it seems to be more of an issue of communication between the Nest and the OTGW. I have no idea if it is due to a Nest update or if something happened to the OTGW after the reset a few months ago. Is there any way to check if the OTGW is still communicating properly?
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Re: Nest Thermostat / Opentherm faulty after OTGW connect

Postby hvxl » Tue Dec 31, 2019 5:13 pm

linezer0 wrote:Is there any way to check if the OTGW is still communicating properly?

http://otgw.tclcode.com/debugging.html
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