Setback override from unknown trigger

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Setback override from unknown trigger

Postby gda01 » Sun Jan 01, 2017 12:44 pm

We have installed the OpenTherm Gateway in our weekend home. (heater: Vaillant hrPRO; thermostat: Honeywell Chronoterm Touch Modulation; Raspberry 2B, OT monitor 4.3, OT gateway 4.2.5, outside temp sensor DS18B20).
The Otgw is operational for a few months. After some initial problems it is pretty stable now. One issue remains however. About once a week we see a Setback constant temp override. We have no idea what triggers this.
I expect a relation with the outside temp sensor, that is, the issue did not appear when the outside sensor was not connected and not configured (GA and GB default value 0).
The now connected outside temp sensor is configured with GA=2 (Vcc) and GB=7 (DS1820) and works fine.
If the Setback function is used, this works also via the GPIO A or B port (config 5 or 6). But in our configuration the GPIO ports are set for the outside temp sensor.
Looking into the Otgw assembler source code, in the main loop the GPIO ports are scanned, and via the GPIO config number a line in a jump table is selected that executes some code. Apparently for some reason not known the code for GPIO option 6 ('Away') is selected, which generates a constant temp override.
From the data in the datalog, no pattern can be found in time and conditions when the override happens.
Anybody any idea or suggestion what might trigger the Setback override ?
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Re: Setback override from unknown trigger

Postby hvxl » Sat Jan 07, 2017 10:11 am

Looking at the code, I don't see how this can happen. Are you sure that it's the setback setpoint that is being activated? If you set it to a different temperature (via the Settings configuration screen or using the SB command), then is that being picked up?

I thought I came up with a clever work-around by setting the setback setpoint to 0. But unfortunately there's a check against that in the code. You could disable that check by commenting out the skpz command in SetSetBack (line 3509 of version 4.2.4 of gateway.asm).

You mention that you use a Honeywell Chronoterm Touch Modulation thermostat. If I remember correctly, that model only accepts remote override setpoints of full degrees. So, as an alternative, you could set the setback temperature to 16.35 or something weird like that. In case the false setback trigger happens then, the gateway will try to set the thermostat to 16.35 degrees. But the thermostat will either go to 16 or not change at all. That is not close enough to the requested setpoint and after a few minutes the gateway will give up and stop sending a remote override setpoint.

So, this work-around may not completely fix the problem, but the wrong setpoint will only last for a short while and then things should return to normal.

This work-around assumes you don't use the regular remote override setpoint. If you do, you'll have to adjust the procedure a little: When you set the remote override setpoint, also set the setback temperature to that same value. When you cancel the remote override setpoint, set the setback temperature to 16.35 again.
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