Nest gen 3 can't start Riello Residence HM in Opentherm

[Carlo]

Hello everyone,

I cannot get the NEST thermostat to work in opentherm with a Riello Residence HM 25 KIS boiler which also supports the protocol (at least from the manual).

I have correctly connected the wires on the boiler PINs indicated as OT+ and on the nest in the relevant OT1/OT2.

Configured from the NEST settings the boiler as opentherm which detects correctly and gives no errors.

The problem arises because I cannot turn on the heaters, just as I cannot set the hot water temperature.
I turn on the thermostat and the boiler does not start, as if it is not receiving input.
The installer has no idea what Opentherm is, have you had similar experiences?

[Carlo]

Hello, everyone,
I'll try to up this post by adding the following:

I did a test with a TADO thermostat which, as soon as it was set up, began to dialogue correctly with the boiler, starting it via the dedicated OpenTherm connection (not ON/OFF).
At this point I am thinking two things, either my nest is faulty or the OpenTherm protocol is implemented partially or differently to TADO.

Does anyone have anything in mind?

Thank you,
Carlo

[luciaaa]

Hi, @Carlo!

Thank you for reaching out to the community. I apologize to hear your Nest thermostat is not working with your heating system. I understand the importance of reliable heating, especially during these colder months. I'm here to help!

To better assist you, please answer the following questions: 

• Is the thermostat displaying any error code? 
• Have you tried to turn on the heat link manually? 
• Does your boiler use OpenTherm for modulation control?
• Has your boiler been modified for OpenTherm compatibility using a third-party add-on module? 
• When did you install the thermostat?
• When did the inconvenience start?

This information will help me to provide you with accurate troubleshooting steps. Thanks in advance. 

Keep me posted.

Best regards,

Ana

[Carlo]

Hi @luciaaa thanks for your reply.

- No, the thermostat doesn't give any error and when configured in OpenTherm it “feels” the connection to the boiler correctly (heatlink connected), same thing for the boiler switching in opentherm on the display.

- Yes, nothing changes

- Yes, it uses OpenTherm and indeed works with TADO in OpenTherm mode (on the contacts for modulation).

- As reported by the manufacturer Riello, the boiler is OpenTherm compatible (Riello Residence HM 25 KIS model).

- The thermostat has been installed for a few years but has always worked in on-off since I had an old boiler. Currently it is still connected in on/off with the new boiler and works properly but I would like to take advantage of the benefits of modulation.

- The problem occurs as soon as I move the wires to the opentherm terminals and set the thermostat to control the boiler with modulation

[luciaaa]

Hi, @Carlo!

Thank you so much for your prompt response; I appreciate all the detailed information provided. 

Certainly, this is not a normal situation where your thermostat doesn't work with your OpenTherm and heating system. To better assist you, the team would like to learn more about this behavior. When you have a chance, please fill out this form and let us know when you're finished. We'll have someone reach out to you via email from there.

Best regards, 

Ana

[Carlo]

Hi @luciaaa thanks, i did it.