Thanks Stefan, great to hear the might be a solution. Gonna try that.
Hi Stefan,
All is working again and thanks for the cooling switch.
Deleting the Mqtt topics was a challenge but eventually it did work, after that some entities changed name so I had to change some of the scripts.
Anyways, I’m up to date with everything working
Menno
Firmware v2.51 is out:
- add dedicated dashboard to webUI
- add status label for cooling status
- add missing bits for fault flags
- add HA control for cooling enable
- add timer table for DHW setpoint
Thanks a lot for this great project. Unfortunately, something doesn’t seem to be working right in my setup. I keep losing the connection in Home Assistant (status switches to “unknown” every minute).
The temperature sensor readings are also fluctuating wildly. Normally, the buffer tank is around 60 degrees, but then OTthing jumps and displays only 30.4 or 2.8 degrees. The log also contains many entries like this:
B701c0000 UKNOWN_ID return_t 0x0000
RX master invalid: 0x110000
RX master invalid: 0x800341ad
RX master invalid: 0x50000
Bc0323ac0 READ_ACK ID 50 0x3ac0
no slave val!
RX master invalid: 0x80100900
T00110000 READ rel_mod 0x0000
RX master invalid: 0x80110000
T00120000 READ ch_pressure 0x0000
RX master invalid: 0x801204fd
Is there anything I can do about this, or is my heating system simply incompatible? It is set to repeater mode. Heating system: Rotex GW TOP with Theta room thermostat.
Besten Dank Manuel
Your Boiler should work aa it says OpenTherm in the documentation. Try a different powersupply and mastermode only if it makes a difference.
Subject: Google Nest V3 + Intergas HRE – using Nest for both heating systems with OT Thing
Hello, Stefan @Phunkafizer
I am considering using an OT Thing with my Google Nest Thermostat V3 / Heat Link and an Intergas HRE 36/30A.
I have a slightly unusual use case and would like to know if OT Thing can do this.
What I want to achieve:
I want to use the Google Nest as the central temperature controller for both my central heating (CV) and my Mitsubishi air conditioners.
Home Assistant will automatically decide which heating system should be active, based on our heating strategy.
The Nest should remain the physical temperature controller in the house.
For example, if the Nest is set to 22°C and I turn the Nest ring to 23°C, Home Assistant should be able to read that the user wants 23°C.
When CV heating is active
Everything should work normally:
Nest → Heat Link → OT Thing → Intergas
If the Nest requests more heat, the Intergas should receive that request normally.
When air-conditioning heating is active
This is the important part.
The Nest should remain fully operational and Home Assistant should still be able to read from it:
current room temperature
Nest setpoint / requested temperature
heating demand / relevant thermostat information
So if I turn the Nest from 22°C to 23°C, Home Assistant should still see that the user wants 23°C.
However, while the air-conditioning heating mode is active, I do not want that heating request to reach the Intergas boiler.
In other words:
Nest → OT Thing → Home Assistant: still visible
but:
Nest → OT Thing → Intergas: central-heating request blocked
The Nest should not know that its heating request is being blocked. It should simply remain a normal, functioning thermostat from the user’s perspective.
The Mitsubishi air conditioners will then provide the heating instead.
When CV mode becomes active again
As soon as Home Assistant switches back to cv heating:
Nest → OT Thing → Intergas
should work normally again.
I do not want to disable or replace the Nest. I only want Home Assistant/OT Thing to temporarily suppress the Nest’s central-heating request while air-conditioning heating is active.
Domestic hot water
An important requirement is that domestic hot water (DHW) must remain completely unaffected.
I only want to block the central-heating demand.
Fail-safe
Another important requirement:
If Home Assistant, the Raspberry Pi or the WiFi connection fails, I want the system to return to normal operation so that the Nest can control the Intergas again.
I do not want a dependency on Home Assistant for basic CV operation.
My questions:
Can OT Thing do exactly this?
Is repeater mode the correct mode for this?
Can OT Thing allow Home Assistant to read the Nest’s requested temperature and heating demand while preventing the heating demand from reaching the Intergas?
Can the CH On / central-heating request be overridden independently from DHW?
Can Home Assistant enable/disable this override dynamically?
When the override is removed, does the Nest immediately regain normal control?
Is this known to work with a Google Nest Thermostat V3 / Heat Link + Intergas HRE 36/30A?
What happens if OT Thing or Home Assistant loses power/network connectivity? Can it automatically fall back to the normal Nest → Intergas connection?
The concept I am trying to achieve is essentially:
CV mode:
Nest → OT Thing → Intergas
Airco heating mode:
Nest → OT Thing → Home Assistant (read only)
while the Nest → Intergas heating request is blocked.
The Nest itself should remain active and continue showing and accepting the user’s selected temperature.
If this is technically possible, I would be very interested in using OT Thing for this installation.
Thank you!
Gr. Robin from Holland
Hi Robin, this is really a very special usecase 
Some things are already possible with the OTthng. E. g. when USB Power is disconnected, the relay will connect the Boiler directly eith the Nest as it would not be present. In repeaer mode you have a switches in HA for overriding some values, e. g. the DHW setpoint, so you could decide from HA if value from Nest or MQtt/HA is used.
Intercepting central heating will not be so easy. The boiler’s outputpower is not controlled by sending the requested room temperature to it. The Nest OR (selectable) OTthing calculates the flowtemperature setpoint by putting requested room temperature and current outside temperature in a formula and sends the calculated result to the boiler (heating curve).
For sure I could add some sensors in HA which always show the setpoints sent by the NEST
Hi Stefan,
Thank you, this explains the OpenTherm behaviour very clearly 
I think I now understand the important part: the Nest does not simply send an “ON” command when the requested room temperature increases. The Nest/heating curve ultimately results in a flow temperature setpoint, which is what the boiler receives.
That actually gives me another idea.
My goal is:
The Nest should remain the user interface for both heating systems.
If I turn the Nest from 22°C to 23°C, Home Assistant should always be able to see that the user wants 23°C.
When CV mode is active, the Nest should work completely normally and its calculated flow temperature should be sent to the Intergas.
When air-conditioning heating mode is active, Home Assistant should still read the Nest’s requested temperature/setpoint, but the Intergas should not provide central heating. The Mitsubishi air conditioners will provide the heat instead.
So I don’t necessarily need to block a simple “central heating ON” command. I understand now that the important value is the flow temperature setpoint.
You mentioned:
“For sure I could add some sensors in HA which always show the setpoints sent by the NEST.”
That would be extremely useful.
Could OT Thing expose in Home Assistant:
The room temperature reported by the Nest
The requested room temperature/setpoint from the Nest
The flow temperature setpoint calculated/requested by the Nest
The actual flow temperature from the boiler
The central-heating demand/state
And most importantly: Could Home Assistant, when air-conditioning mode is active, override the flow-temperature setpoint sent to the Intergas so that the boiler does not heat the house, while still leaving the Nest fully operational and readable?
Then when CV mode is selected again, the Nest’s own calculated flow-temperature setpoint would be passed through normally.
DHW should remain completely unaffected.
If this is technically possible, I think this could be exactly the solution I am looking for.
The desired behaviour would be:
CV mode:
Nest → OT Thing → Intergas
Airco mode:
Nest → OT Thing → HA reads everything
HA/OT Thing → prevents the Nest heating request from causing space heating
OT Thing/HA failure:
Relay bypasses OT Thing and Nest directly controls the Intergas again.
Would this architecture be possible with the OT Thing firmware?
Sorry for all the questions!
Thanks again!
Gr. Robin from Holland
Pretty close, for the full picture: You have 3 essential messages from master to slave (boiler):
- Set DHW temp: Sends the DHW temperature setpoint to the boiler
- Set flow temp: Sends the CH temperature setpoint to the boiler
- Status: This is a bitfield which enabled/disables CH and DHW
When you use the OTthing in mode master with slave interface enabled (for the room unit), you have all values in HA and can do what ever you want. There is a new firmware which additionally exposes all values that the roomunit sends in HA:
Hi Stefan,
Thank you very much for taking the time to explain all this to me, and sorry for all my questions! 
You have already helped me a lot, and I really appreciate it.
I think I now understand the architecture much better.
I just have one last small question, if you don’t mind.
You mentioned that with the new firmware, all values sent by the room unit are exposed in Home Assistant. That sounds perfect for my use case.
Would this allow me to see, for example, the requested room temperature/setpoint from the Nest and the other relevant values that the Nest sends to the OT Thing?
And regarding the three messages you mentioned — DHW temperature, flow temperature and Status (CH/DHW) — am I correct that, in Master mode, Home Assistant can control the CH and DHW status independently?
For my application, the ideal situation would simply be:
Nest remains fully functional as the physical thermostat.
Home Assistant can always see what temperature the Nest is requesting.
In CV mode, the Nest controls the boiler normally.
In Airco mode, HA can disable CH while leaving DHW enabled.
If OT Thing/HA loses power, the relay bypasses OT Thing and the Nest controls the boiler directly again.
If the new firmware already makes the Nest/room-unit values available in HA, that may be all I need.
No need for a detailed explanation if this is already clear from the documentation — I just want to make sure I understand correctly before I buy the device.
Thank you again for your patience and for making such a nice and affordable device!
Best regards,
Robin
Everything yes except one thing: I can not say if the nest sends the room setpoint, this is optional. For sure it sends the flow setpoint as this is mandatory in OT.
Hi Stefan,
I just wanted to let you know that I have ordered the OT Thing!
Thank you so much for all your patience and for answering all my questions. You have been incredibly helpful, and I really appreciate it.
One small thing: you mentioned that the new firmware can expose the values sent by the room unit in Home Assistant. If possible, I would really appreciate it if you could include those sensors/values in the firmware before sending my OT Thing.
Especially the values coming from the Nest/room unit, and of course the flow temperature setpoint that you mentioned.
No need to do anything special if they are already part of the new firmware — I just wanted to remind you before you ship it.
Thanks again, Stefan!
Best regards,
Robin