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OTGW - Thermostat gets disconnected after a few seconds

PostPosted: Sun Aug 26, 2018 3:50 pm
by Luc_S
Hi all,

I soldered an OTGW diy package which worked perfectly for months. After reconnecting the OTGW because of a new thermostat my home was getting heated continuously even though the thermostat was set to 19 degrees and my home temperature was 24+. When the OTGW was removed the issue was gone. Because I didn't have the time and tools to investigate I left the OTGW disconnected for a while.

Today I hooked up the OTGW to a Windows system and noticed that the thermostat is getting some 'T80190000' signals but gets disconnected automatically after a few seconds resulting in 'R00000000' messages (see attachment). When I manually reconnect the thermostat it is again connected, but only for a few seconds.

I tried to troubleshoot using webpage http://otgw.tclcode.com/debugging.html but the measurements seem correct. Then http://otgw.tclcode.com/diagnose.html, I soldered the LED's and they are blinking in order when the first diagnostic test is started. They are however blinking in the exact opposite direction as shown on the page (from right to left). Test 2 is successful until the thermostat gets automatically disconnected again, then there is no result shown anymore. I didn't do any other diagnostic tests.

Has anyone an idea about how to proceed and maybe fix this issue?

Re: OTGW - Thermostat gets disconnected after a few seconds

PostPosted: Wed Aug 29, 2018 8:12 pm
by Cooter
Is your new thermostat listed in the otgw thermostat matrix?

Re: OTGW - Thermostat gets disconnected after a few seconds

PostPosted: Thu Aug 30, 2018 8:31 am
by Luc_S
Yes, the new thermostat is the Quby (Toon) but while hooking it up to the laptop I used my old one which is also in the matrix (AgpoTherm Plus). So the info provided in the topic-start is with the Agpo thermostat.

Re: OTGW - Thermostat gets disconnected after a few seconds

PostPosted: Thu Aug 30, 2018 9:17 pm
by hvxl
The Diagnostics window is only supposed to be used with the diagnostic firmware. It is not very useful when used with the normal firmware. In that situation, you get much better information by looking at the Log tab.

T-messages are reports of what the thermostat is sending, not what it is getting. But there are no B-messages, so the boiler doesn't appear to respond.

It is unclear if the thermostat stops sending messages due to the lack of responses and switches to on/off mode, causing the "Thermostat disconnected" message, or if the voltage on the thermostat interface is close to the threshold and the disconnection detection is falsely triggered.

To check, you can use the command DP=57. This will report the measured line voltage after each message. A connected opentherm thermostat should normally result in values between 6 and 122. Values outside that range are assumed to be caused by the thermostat being disconnected, or using an on/off thermostat.

Re: OTGW - Thermostat gets disconnected after a few seconds

PostPosted: Sat Sep 01, 2018 6:03 pm
by Luc_S
Ah ok, clear. Well the boiler wasn't connected at all. I just thought I could troubleshoot with the OTGW and old thermostat first and then noticed the automatic disconnects. I had no idea the disconnect could be a result of an absent boiler.

Because of my holiday I won't be able to test this right now but I will report back once I checked this out. Thanks!

Re: OTGW - Thermostat gets disconnected after a few seconds

PostPosted: Sat Sep 01, 2018 8:09 pm
by hvxl
I don't know if the absence of a boiler is the cause of the disconnect in this case. But I know there are thermostats out there that will switch to on/off mode if they don't get an opentherm reply within a certain amount of tries after startup. So it's a possibility. More data will be needed to make sure.

The opentherm spec actually prescribes that a master should first try to use OT/+ communication. If no valid response is received for 20 seconds, it should switch to OT/- mode, which is basically on/off mode. Your screen shot shows 20 attempts before the "Thermostat disconnected" message. Coincidence?