NEST 3 compatability w/OpenTherm

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NEST 3 compatability w/OpenTherm

Postby wfh118 » Tue Dec 27, 2016 4:12 am

I am trying to install a NEST 3 UK version on a BAXI LUNA HT 330 Combi. The interface is Siemens OpenTherm motherboard 567715.2 using a QAA73.110 controller. Boiler installed in 2006. Installation of Nest and Heat Link unremarkable. Thermostat initiated properly, recognizes OT interface present (radiant floor heat), but in the test (and repeatedly), the set thermostat believes the boiler is running, predicting time to temperature attained. Nothing is happening at the boiler. Test times out. Run troubleshooter but no errors are posted. Am I experiencing an incompatibility issue? If so, are there any feasible solutions?
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Re: NEST 3 compatability w/OpenTherm

Postby wess51 » Sun Jan 15, 2017 8:33 am

I have same issue with Nest 3rd gen and BAXI 1400. My system also equipped with OpenTherm interface and QAA.73. After installing and trying to do some tests, there's no reaction from boiler. I can't imagine what we do wrong...
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Re: NEST 3 compatability w/OpenTherm

Postby handycam » Wed Jul 19, 2017 11:39 pm

I am in the same boat -- Baxi Luna HT 330 Combi and Nest UX v3. Same symptoms. Contacting Nest for help but no resolution so far. Any chance you figured out what the issue is?
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Re: NEST 3 compatability w/OpenTherm

Postby handycam » Wed Aug 02, 2017 3:34 pm

I think I have resolution to the Baxi Luna HT 330 and Next UK v3 after getting some good information from Baxi and being chided by Nest for not using a Nest Pro installer.

Feedback from the very helpful Baxi team:
“Unfortunately the OpenTherm world is more complicated that what it seems, below I will try to explain the reasons.

First of all we must differentiate the Open Therm (OT) protocol from the Open Therm Standard (OTS) protocol, this difference is really important because the OTS has defined and specific rules, where to obtain the OTS, you must respect every ID data point one by one. In this way, if all the producers respect the ID data points, any type of device can communicate without any problem or conflict.

When we are using the OT, as in Luna HT 330, the ID data points may be not in the same position of the ones set, in this case by Nest, in this case we can't guarantee full compatibility of the communication. Some functions could work well and while some others may not at the same time.

To explain better I’ll make an easy example:
Baxi OT should be set with ID1= Heating function, if set to 0 it means the Heating function is disactivated, if set to 1 it means the Heating function is activated;
Nest OT should be set with ID1= DHW function, if set to 0 it means DHW function activated, if set 1 it means DHW function is disactivated.

As you can understand, when from the Nest control we activate the DHW function the ID1 value changes from 1 to 0 and is transmitted to the boiler; in this moment the boiler receives the information and changes ID1 from 1 to 0 but, on Baxi OT, this mean to disactivate the Heating function.

Clearly this seems to be a problem on the boiler because it makes a different result from what is required from the Nest control but in reality it’s "just" a not fully compatible between the 2 devices. Unfortunately has been test no real test data between the two.
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Re: NEST 3 compatability w/OpenTherm

Postby D_Hailsham » Mon Aug 07, 2017 10:22 am

Don't understand what the Baxi guy means by OT Protocol and OTS Protocol. I always thought there was only one Protocol. Though it could be that he is talking about a Baxi-specific version of OpenTherm, so customer are forced to buy both boiler and thermostat from Baxi. That makes me wonder if the devices can then be called OpenTherm compatible. I wonder what the Opentherm Association's reaction will be?

The UK Baxi website has this to say about OpenTherm, which seems to contradict what you have been told:

OpenTherm is a system of communication which is not specific to any particular manufacturer. It allows boilers and controls to communicate information from one to the other. Products which are optimised for OpenTherm will display the logo.

Your Baxi guy has his ID's muddled! ID=1 is the Control Setpoint (flow temperature).
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Re: NEST 3 compatability w/OpenTherm

Postby marcelr » Tue Aug 08, 2017 6:31 pm

Baxi are not a member of the OpenTherm society. Probably their OT interfacing is handled by Remeha, with whom they have a strong cooperation. The answer you got from them is totally wrong. ID0 holds the selection bits for boiler control, whereas ID1 sets the boiler output temperature. Other Baxi devices are reportedly supported by hvxl's OTGW, so the Baxi engineers at least CAN get it right. Not sure if that's the case in your model.
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