OT Thing - An OpenTherm-WiFi Gateway with integrated OT master & slave

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41

Hi Stefan,
Thanks again — I think I’m starting to understand better now.
So just to confirm:
• In repeater mode, it won’t work because Wiser doesn’t send any DHW message at all — so there’s nothing for OT Thing to modify.
• In master mode, if OT Thing could listen to Wiser as a slave and “adopt” the heating setpoint while injecting its own DHW setpoint, then it might work — but that logic isn’t implemented yet, right?
Would you say this setup is something you’re confident could work with a bit of development? Or is it still uncertain whether it would behave reliably?
I’d be more than happy to buy and test it if we’re reasonably sure it could work — but if it’s still speculative, I’d rather avoid the shipping hassle for now.
Thanks again for your time and explanations — really appreciate it!

42

Yes Aron, you got it. I think implementation is not that hard and can be implemented quickly.

43

Hi Stefan,

Thanks again for your detailed explanations — I really appreciate your time and clarity.

I’ll hold off on ordering for now and let you work on the potential implementation. Once it’s confirmed that the setup with OT Thing in master mode (adopting Wiser’s heating setpoint and injecting a fixed DHW temperature) is working reliably, I’d be happy to purchase and test it.

I’ve also reached out to Drayton to see if they can confirm whether Wiser sends any DHW-related OpenTherm frames at all — just to be thorough.

One last question: in this configuration, if OT Thing were to fail or lose power, would the system automatically fall back to Wiser communicating directly with the boiler? Or would a manual bypass be needed?

Thanks again — looking forward to hearing more when you’ve had a chance to explore it!

44

If OT thing looses power the relay would automatically fall off and connect the room unit with the boiler.

45

Hi Stefan,

Thanks again — that’s great to hear!

I’ll hold off on ordering for now and let you explore the implementation. Once you’ve had a chance to test and confirm that the setup works reliably — with OT Thing acting as master to the boiler while also adopting the heating setpoint from Wiser via its slave interface and injecting a fixed DHW temperature — I’d be happy to purchase and help test it.

Also, thanks for confirming that the relay would automatically fall back to connecting Wiser directly to the boiler if OT Thing loses power — that’s reassuring and exactly what I was hoping for.

Looking forward to hearing more once you’ve had a chance to work on it!

46

It seems to work. You will have to configure OT Thing like so:

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47

Hi Stefan,
Sorry for the late reply - that’s fantastic news! :blush: I’ll go ahead and order it soon, just need to sort out an EU drop-off address first.
Quick question: what’s the usual lead time for shipping to the EU? I’d love to plan things so it arrives in time for a test install. Also, any idea how big the parcel is? Just want to make sure it’s something my friend can easily receive.
Thanks again for all your help and development work - really appreciate it!

48

lead time is ~3 days and the parcel is about 15x10x5 cm.

49

hello, nice work @Phunkafizer , wondering if you have added the outsidetemperature sensor connected to the boiler to the firmware so that it can be selected as the source for outsidetemperature? Thanks

50

Yes the outside temperature sensor of the boiler can be selected and used for the calculation of the flow tempeature.

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51

I need BOM and gerber films thanks

52

In the GIT repository you can find the KiCad project of the PCB.

53

Hi Stefan!

I would like to purchase the OT Thing board from your website. But, I would like to know your opinion on 2 things:

  1. Is it compatible with IMMERGAS VICTRIX TERA V2 35 Plus EU - 35 kwh?
  2. The 1 wire port, how many sensors can I use? Is it possible to add like 14 of them?I would like to use ds18b20 (https://sigmanortec.ro/Senzor-sonda-temperatura-impermeabil-DS18B20-DSB18B20-p126400819?SubmitCurrency=1&id_currency=2)

–
You did a great job with this project! I might be order the gas meter as well.

54

Thanks for your interesst! With this boiler unfortunately I don’t have any experience, you only can try. If you have a room unit there are good chances as it can be used as reference.
The number of sensors heavilly depends on wire length and topology, if you keep it short and in bus topology it could work, additionally decreasing the pullup resistor could help.

Regards
Stefan

P.s. Interessting links for 1wire setup:
https://www.analog.com/en/resources/technical-articles/guidelines-for-reliable-long-line-1wire-networks.html

55

Firmware v2.9 is available:

  • add OTC, summer mode & DHW blocking for boiler
  • auto selection for roomsetpoint source
  • round 1wire values
  • Configuration of statusrequest for immergas boiler

Release can be downloaded from github:

56

Firmware v2.10 ist available:

  • configurable hostname
  • display num WiFi & MQTT disconnects
  • configurable MQTT keep alive
  • log MQTT disconnections ith reason
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57

Hello,

I purchased and started to use your module. It looks and works great, big thank you for such development. I have one little ask for you: is it possible to make discovery prefix for HA configurable? It’s hardcoded to “homeassistant” right now and my existing ecosystem has additional level on it, thereby the discovery is not working.
Thank you in advance!

58

see release v2.11, HA discovery prefix is now configurable.

59

Wow, you are fast! I have installed and tested it, works as expected. Thank you very much!