In need of a thermostat?

This Forum is about the Opentherm gateway (OTG) from Schelte

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In need of a thermostat?

Postby kaspberry » Thu Nov 05, 2015 3:48 pm

Since i don't get any information in my topic about an Opentherm Gateway and a Raspberry pi i just bought the stuff.

I want to control the Nefit Trendline boiler from my Raspberry Pi Home Automation system (Programmed by myself). I want to send the current room temperature, outside temperature and set temperature to the boiler. Programs are controled by the raspberry pi (When what temperature is needed).

Do i need a thermostat to control the boiler via modulating? And if so, what will be the best thermostat for my needs?
Ik hope someone can help me a little more.

I tried connecting a ICY smart thermostat to the opentherm gateway and i could read some data (room temperature, set temperature), but if i want to override the set temperature, nothing happens.

Thank you very much!
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Re: In need of a thermostat?

Postby hvxl » Thu Nov 05, 2015 6:12 pm

You may think it's easier to ask than to look for an answer yourself. But I have better uses for my time than to answer the same question umpteen times. So with the latter method you will probably achieve your goal faster.
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Re: In need of a thermostat?

Postby kaspberry » Thu Nov 05, 2015 7:04 pm

I don't have to ask questions if i find the awnser but i tried and searched online but still can't find the awnser.
I guess you (and other forum visitors) have much more experience than i do and can quickly tell me what's the best way.

I also guess you? (or an other forum member) are the developer of the board so if i buy something i want to know if the thing i want to do with it is possible.
There is not that many information available and as there is a forum, i'm using it for where it's meant to

Thanks for your reply!
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Re: In need of a thermostat?

Postby marcelr » Thu Nov 05, 2015 10:50 pm

You will need a thermostat to drive the boiler. I don't know your specific boiler hardware, therefore I cannot say which thermostat works best, but an OTGW is definitely not going to do it for you. Nefit are notorious for NOT supporting OT. Only some of their latest boilers have an OT interface, for somewhat older types you can revert to their EMS-OT converter.

No offense, but I think Schelte means to tell you that you should dig a bit deeper into boiler types and boiler control options, the OT protocol, and what you can and cannot do with it before rushing into a boiler control adventure. It may be not as simple as you might think it is, I'm not sure what your exact plans are. The information is readily available, Google is your friend when it comes to that ...

good luck,

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Re: In need of a thermostat?

Postby Akatar » Thu Nov 05, 2015 10:53 pm

some nefits are talking ot and some of them need an extra pcb,
ans some will never talk ot

http://www.homewizard.nl/nefit-opentherm-converter.html
i own the extra pcb and mine is working fine with ot
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Re: In need of a thermostat?

Postby hvxl » Thu Nov 05, 2015 11:45 pm

What I mean is that using the gateway without a thermostat has been discussed before, for example here and here. After actually having looked those up, I have to admit they were harder to find than I expected. But on the question of which thermostats work with the gateway, and to which extent, there is even a dedicated sticky topic. If someone claiming to be looking for "the best thermostat for my needs" hasn't found that, it's difficult for me to believe he has been looking very hard.
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Re: In need of a thermostat?

Postby kaspberry » Thu Nov 05, 2015 11:49 pm

Thanks for all your replies,

I do have the Nefit Openther Converter. I want to control the boiler (Nefit Trendline HRC30 CW5). I intended to do it without thermostat (and use the raspberry pi as a thermostat), but i now see it's not the good way. I think i can use the Raspberry Pi to send the signal to the thermostat (Via the Opentherm Gateway), and let the modulating thermostat control the Nefit Trendline via the Converter (Am i thinking right?)

Then the Honeywell Chronotherm Modulation thermostat can do what i want i guess? (i know you just told there is no "best" thermostat, but maybe you know that this one won't work for my needs, or you know it will work)
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Re: In need of a thermostat?

Postby kaspberry » Fri Nov 06, 2015 1:46 pm

I'm sorry to post another question but i have read manuals and can't find my awnser. Maybe someone knows.

I am willing to buy a Honeywell Chronotherm 4 but i would like to know if it's possible to override the current termperature? This because i don't want to have the thermostat hanging in the livingroom but near the boiler just to use it for modulating. By a raspberry i want to set the measured temperature to the chronotherm. Will this be possible? (Maybe also outdoor temp?)

I have seen in this topic (viewtopic.php?f=75&t=10541) that the setpoint can be send to the thermostat, but i can't find if the current temp and / or outside temp can be set


Thank you very much!
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Re: In need of a thermostat?

Postby hvxl » Sat Nov 07, 2015 3:44 pm

Beware that a Chronotherm 4 is an on/off thermostat. It is of little use with the OTGW. I presume you mean a Chronotherm Modulation T8851M.

The outside temperature can be sent to the T8851M. I don't think it uses this for anything other than displaying it.

I have to admit that I never tried to send a different room temperature to a thermostat. So I can't say for sure that it won't have any effect, but I would be very surprised. It's an interesting idea though.

UPDATE: I did a test bench trial and can now confirm that the T8851M doesn't pick up the room temperature value provided via opentherm. Neither does the Honeywell round modulation, by the way.
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Re: In need of a thermostat?

Postby kaspberry » Sat Nov 07, 2015 5:50 pm

Thank you, i meant the T8851m like you said.
I think i'm going to buy a second hand one and try to remove the temp sensor and place a cable between since i don't want to place the thermostat in a visible position.

I hope i find the thermometer and it will still work afterwards.


Thanks for your testing!
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Re: In need of a thermostat?

Postby hvxl » Sat Nov 07, 2015 10:02 pm

The T8851M has two connections marked RT. I think their purpose is to connect a remote temperature sensor. But getting the specifications for such a sensor may be a challenge.
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Re: In need of a thermostat?

Postby kaspberry » Sat Nov 07, 2015 11:25 pm

I mean using the built in temperature sensor?

I can remove the temp sensor sensor, solder a cable between and place the temp sensor on another place then the thermostat, this will work won't it?
Maybe someone has a picture of the pcb of the T8851M?

Thanks again!
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