Egyras
Opentherm with NEST
Hello,
Has anyone manage to get Opentherm working with a NEST device ? I've seen post of people that have Opentherm working with other devices, but none with a NEST.
And in my configuration I am not being able to communicate with the NEST (regardless of the cable length or connection) These are my logs regarding OpenTherm:
Wed Jun 4 14:03:36 2025 (412292696): OpenTherm: Received read slave config
Wed Jun 4 14:03:36 2025 (412292991): OpenTherm: Received DHW set boundaries request
Wed Jun 4 14:03:36 2025 (412293252): OpenTherm: Request invalid!
Wed Jun 4 14:03:37 2025 (412294214): OpenTherm: Received CH set boundaries request
Wed Jun 4 14:03:38 2025 (412294508): OpenTherm: Request invalid!
Wed Jun 4 14:03:38 2025 (412295403): OpenTherm: Request invalid!
Wed Jun 4 14:03:39 2025 (412296390): OpenTherm: Read request DHW setpoint
Wed Jun 4 14:03:40 2025 (412296659): OpenTherm: Request invalid!
Wed Jun 4 14:03:41 2025 (412297588): OpenTherm: Read request Max Ta-set setpoint
Wed Jun 4 14:03:41 2025 (412297849): OpenTherm: Request invalid!
Wed Jun 4 14:03:42 2025 (412298810): OpenTherm: Received status check: 0, CH: 0, DHW: 0, Cooling, 0, OTC: 0, CH2: 0, SWMode: 0, DHWBlock: 0
Wed Jun 4 14:03:42 2025 (412298811): OpenTherm: Send status: CH: 0, Flame:0, DHW: 0
Wed Jun 4 14:03:42 2025 (412299104): OpenTherm: Request invalid!
Wed Jun 4 14:03:43 2025 (412300032): OpenTherm: Received read slave config
Wed Jun 4 14:03:43 2025 (412300326): OpenTherm: Request invalid!
Wed Jun 4 14:03:44 2025 (412301255): OpenTherm: Received DHW set boundaries request
Wed Jun 4 14:03:45 2025 (412301549): OpenTherm: Request invalid!
I am using the heishamon large version from TheHogNL, running FW 3.9
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I will try to get a 2nd hand NEST myself and try to figure out what is wrong. Can you tell me which NEST model/type you have? I am not familiair with NEST models/types
Anyway, it does seem to receive some information but also some invalid requests. Don't you see any information in the opentherm tab on the heishamonw website?
That would be greatly appreciated. I have a Nest Thermostat 3rd generation.
Thermostat Model : Display 3.4 Backplate model : Backplate 6.5
Heatlink: Model Amber 2.5
I do have some information and invalid requests, as I shared in my first post, just dont really know what to do with it... In the opentherm tab every things seems to be 0 or not connected:
This issue is stale because it has been open 30 days with no activity. Remove stale label or comment or this will be closed in 5 days.
I am still interested and open to help with this issue. Please dont close :)
This issue is stale because it has been open 30 days with no activity. Remove stale label or comment or this will be closed in 5 days.
This issue is stale because it has been open 30 days with no activity. Remove stale label or comment or this will be closed in 5 days.
@emilic14 just got myself a 2nd hand gen 3 nest thermostat and hooked it up to a test heishamon. It works fine. Your logs do seem to show it does work for half of the time but you do have some requests invalid. This could mean that the opentherm line from heishamon to the nest heatlink is receiving some external noise
@IgorYbema thank you so much for checking this! Ok so if I understand correctly either the cable I am using is faulty, or too long ?
Is there any specs of info of the length and quality of the cable I should use for Opentherm to work correctly ?
Thank you
I don't know that. I tested only with a small length cable. Maybe you can test it also with a small cable and see if that improves it so you know it is indeed the cable?
Hello! I can confirm, a smaller cable and now I no longer see the error! :) I am actually using an repurposed Ethernet cable that is insulated, so I think that helps with the external noise.
But, the reported temperature on Opentherm is not the one reported on my Nest device... So not sure if I am missing something in the configuration, but @IgorYbema does your Nest share the temperature information in your Opentherm setting
I didn't check that but the information is not real time. It can take a while (like a minute or so) for opentherm to send data which just change like a temperature. But the roomTemp should be the one Nest is reporting
Yeah, noup... roomTemp is stuck at 20 I'll keep on checking but even if the communication seems a lot better now, even after 2 days the roomTemp has not changed but it is changing on the Nest side.
can you please check the log for a line like this:
Tue Nov 18 15:54:17 2025 (1989912924): OpenTherm: Room temp: 19.9141
It took a minute or two for me to see that in the logs (not a Nest thermostat though). And what other opentherm messages do you receive now?
Noup... these are my logs (without dates etc)
OpenTherm: Read request DHW setpoint OpenTherm: Read request Max Ta-set setpoint OpenTherm: Received status check: 0, CH: 0, DHW: 0, Cooling, 0, OTC: 0, CH2: 0, SWMode: 0, DHWBlock: 0 OpenTherm: Send status: CH: 0, Flame:0, DHW: 0 OpenTherm: Request invalid! OpenTherm: Received read slave config OpenTherm: Received DHW set boundaries request OpenTherm: Received CH set boundaries request OpenTherm: Read request DHW setpoint OpenTherm: Read request Max Ta-set setpoint OpenTherm: Received status check: 0, CH: 0, DHW: 0, Cooling, 0, OTC: 0, CH2: 0, SWMode: 0, DHWBlock: 0 OpenTherm: Send status: CH: 0, Flame:0, DHW: 0 OpenTherm: Received read slave config OpenTherm: Received DHW set boundaries request OpenTherm: Received CH set boundaries request OpenTherm: Read request DHW setpoint OpenTherm: Read request Max Ta-set setpoint OpenTherm: Received status check: 0, CH: 0, DHW: 0, Cooling, 0, OTC: 0, CH2: 0, SWMode: 0, DHWBlock: 0 OpenTherm: Send status: CH: 0, Flame:0, DHW: 0 OpenTherm: Received read slave config OpenTherm: Request invalid! OpenTherm: Received DHW set boundaries request OpenTherm: Received CH set boundaries request OpenTherm: Read request DHW setpoint OpenTherm: Read request Max Ta-set setpoint OpenTherm: Received status check: 0, CH: 0, DHW: 0, Cooling, 0, OTC: 0, CH2: 0, SWMode: 0, DHWBlock: 0
So still trying two things :
- the cable I am used is shielded but the shield is not grounded. Is this something that may be causing the invalid requests? -> Note the cable I used to test is about 10cm long...
- the configuration of my Nest, not sure if I need to configure the opentherm or something else... Documentation is not great on the Nest side, they always send you to check with a Pro...
Yes you need to set to 'custom' and then select opentherm. But it already seems to talk opentherm so I think it is already selected correctly. Not sure why it isn't giving back the current room temp. I'll check my nest when I have time
Hello,
Yes I believe Opentherm is well set up in heishamon. My question is more on the Nest part... although I did go to advanced pro settings and stated a heat pump using opentherm for radiators...
I also just swaped the cables to place OP1 -> Connector 1 of heishamon and OP2 -> connector 2 of heishamon... to OP1 -> Heish 2 and OP2-> heish 1; and no big change, getting the same result, so I am guessing that the connection of the opentherm cables and heishamon makes no real difference... I am out of ideas ^^
Hello,
Yes I believe Opentherm is well set up in heishamon. My question is more on the Nest part... although I did go to advanced pro settings and stated a heat pump using opentherm for radiators...
This is what I meant to say to check this in the Nest. I didn't find time to check this yet on my Nest so please be patient
I have tried for months and could get it to work. Even with the thermostat next to the Heishamon lots of invalid requests. The data it does receive does not make any sense or is locked to a specific value. On occasion the thermostat also gives the error that it can't control this boiler. In the end i ditched it completely and used the google api to get the temperature readings in MQTT.
I have tried for months and could get it to work. Even with the thermostat next to the Heishamon lots of invalid requests. The data it does receive does not make any sense or is locked to a specific value. On occasion the thermostat also gives the error that it can't control this boiler. In the end i ditched it completely and used the google api to get the temperature readings in MQTT.
Good to know that I am not the only one ^^