Unresponsive OTGW defaults to heating with max values

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Unresponsive OTGW defaults to heating with max values

Postby EP94 » Wed Oct 13, 2021 6:39 pm

I have my own created domotica system and a smart thermostat is one component of it. I have an OTGW connected to my boiler, and a Raspberry Pi connected to the OTGW.

I used to have a ESP8266 connected to the OTGW and the raspberry pi connected to the ESP8266 through a TCP connection. I believe it happened after an update from version 4.3 to version 5.1, but i don't know for sure, but at one moment, the OTGW became unresponsive, turning on the boiler with a boilersetpoint of 90 degrees and a max modulation level of 100%. I was at home by then so I could respond to the event. I pulled the plug of the OTGW and put it back in, and everything started working as normal.

After that event i thought i needed to have more control over the OTGW, so i bought a FTDI cable so i could connect the Raspberry Pi directly via USB instead of wifi. Still, after a while the OTGW becomes unresponsive, and turning on the boiler with a boilersetpoint of 90 degrees and a max modulation level of 100%.

Does anyone have an idea where to start or how to debug or fix this? As far as i'm concerned there are two problems; the OTGW stops responding after a while, and the OTGW defaults to heating with the max possible values.
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Re: Unresponsive OTGW defaults to heating with max values

Postby hvxl » Thu Oct 14, 2021 10:25 am

I don't completely understand what is going on. You say that the OTGW becomes unresponsive. Then how do you know the boiler is turned on "with a boilersetpoint of 90 degrees and a max modulation level of 100%"? If by unresponsive you mean that it doesn't react to commands anymore, but still reports messages, then a log would probably be very helpful.

If there is no more output from the OTGW and you just notice that the boiler switches on, this may be due to the so-called "Special Installation Short-Circuit Feature" defined as part of the Opentherm protocol. This feature says that a "boiler unit should interpret the short-circuit as a heat demand within 15 secs of the short-circuit being applied" and "It is allowable that this can implemented by a software-detection method. The software short-circuit condition is defined as a low-voltage state (Vlow) with no valid communications frame for at least 5 seconds."
This means that the boiler may interpret the idle state of the Opentherm signal as a heat demand if it persists for more than 5 seconds. This situation might occur should the OTGW become unresponsive and stops sending messages. For this reason, the OTGW has measures to prevent this. If the firmware gets stuck, a watchdog will kick in and reset the device. If the connected thermostat stops sending messages for some time, the OTGW raises the output to the boiler to Vhigh. If the thermostat is disconnected, the OTGW starts generating its own Opentherm messages.
In this case the most important thing is to figure out why the OTGW stops responding.
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Re: Unresponsive OTGW defaults to heating with max values

Postby EP94 » Fri Oct 15, 2021 11:33 am

Thank you for your reply.

I'm sorry if i didn't explain it correctly. By unresponsive i mean both: the OTGW doesn't respond to messages and doesn't produce messages. The 100% modulationlevel is an assumption, but normally the control setpoint is around the 60 degrees (except on very cold days, which it wasn't). After the reboot of the OTGW, all things were working correctly, and the water temperature was around the 90 degrees. I also monitor the gas usage, and the heat-cyclus used a lot more gas than usual (with a controlled max-modulationlevel).

The "Special Installation Short-Circuit Feature" you're describing is pretty much what i'm experiencing, except for the fact that it doesn't reset (or recover) itself. The only way to fix it, is to pull the plug. Is it possible, that under certain curcumstances the watchdog doesn't kick in? I don't have a thermostat connected, as i've written my own.

I currently have an OTMonitor running constantly, so if it happens again, i can send the logs that were sent just before the event.
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Re: Unresponsive OTGW defaults to heating with max values

Postby hvxl » Fri Oct 15, 2021 2:12 pm

The watchdog kicks in when the firmware gets stuck executing code that doesn't reset the watchdog timer. The watchdog timer is only cleared during initialization, in the main loop, and in the self-programming code. The main loop is where the timer is normally reset when the OTGW is running. The initialization code runs before the program enters the main loop. It can only get stuck there if timer 0 somehow gets reconfigured. That is very unlikely to happen spontaneously. If the PIC managed to jump into the self-programming code, it may not get out on its own.

Do you have LEDs on your OTGW? What do they indicate when the OTGW becomes unresponsive?

Also, what do you mean when you say you've "written" your own thermostat? When referring to a thermostat, I picture a piece of hardware. So the usual verb associated would be "build", not "write". Or is the OTGW your hardware interface, and it's running the "interface" firmware? That completely changes the situation.
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Re: Unresponsive OTGW defaults to heating with max values

Postby EP94 » Fri Oct 15, 2021 2:34 pm

The "thermostat" is a piece of software running on the raspberry pi, acting like a thermostat (by controlling the boiler setpoint, max modulation level and of course the central heating enabled bit based on the room temperature).

The OTGW is the one from the NodoShop, so it does have LED's. Currently, if the event occures the "thermostat" will reset the OTGW itself by toggling the outlet off and on, so it is kind of hard to look at the LEDS at the moment, as i don't know when it will occur. If it happens when i'm not home, the gas bill will be very high that month as i won't be able to reset the OTGW.

I don't use the interface firmware(do you recommend this in my situation?) I use the gateway firmware version 5.1.
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Re: Unresponsive OTGW defaults to heating with max values

Postby hvxl » Fri Oct 15, 2021 3:44 pm

So the OTGW runs stand-alone and your thermostat software sends it CS, MM, and CH commands? I'm just trying to get a clear picture of the setup.

If that provides you with enough control, then there's no reason to switch to the interface firmware.
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Re: Unresponsive OTGW defaults to heating with max values

Postby EP94 » Sat Oct 16, 2021 8:06 am

So this were the logs just before the connection was lost:

< 07:00:34 - everything normal

07:00:34.331335 z?Z????<xT
07:00:34.366407 y????1_?????
07:00:34.383577 ?A

After that the OTGW stopped responding.
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Re: Unresponsive OTGW defaults to heating with max values

Postby hvxl » Mon Oct 18, 2021 8:39 pm

I would think it is obvious that this is a useless log, if you can even call it that. You removed all the actual data that may contain useful clues and replaced them with your high-level interpretation of the situation. That makes it impossible for me to understand what was going on at the time the problem started. So, based on the information you provided, I can't offer any help.
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