OpenTherm Boilers and Controls

57 thoughts on “OpenTherm Boilers and Controls”

1. My boiler is a Vitodens 100-W Type B1HA, B1KA, 6.5 to 35Kw Wall mounted condensing boiler.
   It is not on your list of OT compliant boilers.
   The installation instructions suggest that it is compliant and I am hoping you can confirm one way of the other.
   Thanks
   Paul Cracknell

   Reply

   1. Hi Paul,
      We have checked the instruction manual, it clearly shows on page 22, that it supports opentherm. We have updated the list to reflect this. Please note, we cannot state the effectiveness as manufacturer implementations of OpenTherm vary between boiler brands, as has been reported by various specialists, so the performance of the OpenTherm setup may also vary. Please feel free to report your results

      Jayesh.

      Reply

2. Excellent article! In your ”unofficially compatible” list sits my Glow-worm Ultracom, which you mention will require an adaptor. Apologies if I’ve missed it within the above, but do you have any more info/links to such adaptors? The Climapro2 controller we currently use is starting to play up so I’m looking at alternatives. Thanks, Andy.

   Reply

   1. Hi Andy,

      Have a look at the following article Vaillant Opentherm/, as the Vaillant and Glowworm share the same PCB they use the same adapters. Most likely for the Ultracom is the VR33 0020017895 / equivalent AWB 0020092426 or the AWB OPENTHERM MODULE 0020036768 for certain Glowworm Boilers. Search these parts and look at the inside of your PCB housing to determine which is the correct one. Hope that helps.

      Jayesh Kanbi

      Reply

3. Hi i have recently installed a Baxi Platinum combi which does not appear on any of your lists? I know this is a modulating boiler but i’m not sure if this means its opentherm compatible.

   Can you please confirm if this boiler is able to use opentherm?

   Reply

   1. Hi, the Baxi Platinum boiler is not OpenTherm compatible. Most modern condensing boilers are internally modulating ie room controls ask a boiler to come on off, the boiler determines it’s own power level. Where as an opentherm boiler is told by opentherm controls what powerlevel it should be at. Hope that answers your question.

      Reply

      1. Is there a way of making the Baxi Platinum boiler OpenTherm compatible? Any sort of aftermarket adapter or PCB/controls update/upgrade?
         I have the same boiler and a Nest 3rd generation thermostat and it’s a shame that it doesn’t support OpenTherm.
         Many thanks.

         Reply

         1. Hi, there is no OpenTherm support on this boiler. You can use smart trvs and controls such as Tado to try and gain some efficiency. Apart from that, there is no simple way to do modulation. There may be complex ways to modulate the boiler externally, however these are outside the scope of most installers and generally not worth the extra complexity introduced. JK

            Reply

4. Hi,

   Do you know whether the Ideal Combi ESP1 35 supports Opentherm ?

   Regards,

   Patrick.

   Reply

   1. Hi, Thank you Patrick.

      Boiler added to list, credit given to you for help.

      Regards,

      Jayesh Kanbi
      MyBoiler.com

      Reply

5. George Arnautu,
   Hi, I have a Viessmann boiler, Vitodens 111 – W, type B1LA-26 , and I don’t know whether tthe SALUS thermostat RT520 RF is Opentherm compatible,
   Thanks,
   George Arnautu

   Reply

   1. Hi George,

      This control definetely has OpenTherm, please see following link. https://salus-controls.com/uk/product/rt520/#downloads , select the quick guide to show you the connection diagram.

      Regards,

      Jayesh Kanbi
      MyBoiler.com

      Reply

6. Veissmann vitodens 050 w supports opentherm.

   What would be more useful is to know what commands and data boilers support as it seems the spec allows for a lot of data which not all boilers support.

   Reply

7. Hi there. Just moved in to my new flat. How can I find out if worcester greenstar 28i junior is opentherm or not ???

   Reply

   1. Hi Mickey, it’s not OpenTherm out of the box. There does appear to be a work around , however not widely tested. See the following article https://myboiler.com/opentherm/worcester-bosch-opentherm/ If that seems complicated, I would suggest contacting Tado as it is able to work with a wide range of boilers in modulating control mode, as well as having an OpenTherm interface. The other alternative is to use Worcester Wave to allow app control as well as modulating the boiler similar to OpenTherm. If you need more info, fill in the contact form and send a message. Hope that helps.

      Reply

8. Hi is the Viessman Vitodens 111 35kw OpenTherm Compatible?

   Reply

   1. Hi yes it is. See page 15 of the Installation and Servicing manual.

      Reply

9. Hi
   I had a new boiler installed last year without any smart thermostat installation as I did not like any of their offerings.
   1. I have a Worcester Bosch Greenstar 27Ri Compact ERP. Do you know if this is Opentherm compatible?
   2. If it is, do you know of a smart thermostat that is uses Opentherm within a Zwave network as I am thinking to invest in Zwave network to reduce the load on my every increasing Wifi network?

   Reply

   1. Hi Kai,

      1. The boiler you have is not known to be OpenTherm Compatible.
      2. I would suggest to go to https://www.automatedhome.co.uk/vbulletin/ Forum to see of any Z Wave devices that may work for you. Also I found another one that is https://www.uk-automation.co.uk

      Hope that helps.

      Jayesh, MyBoiler Ltd

      Reply

10. Hi,
    I have a Glow Worm Ultimate 35C, it’s getting on a bit now but still going strong, I used to have a climapro2 thermostat connected to it via the bus connection. It worked very well until it got dropped and screen cracked so I decided to upgrade to a nest 3rd generation. My question is would I be able to use the nest with OpenTherm or would I only be able to use it to start/stop the boiler? If OpenTherm is possible what extra adapter would I need if any?
    Thanks in advance
    Kind regards
    Jonny

    Reply

    1. Hi Jonny,

       Please read the following article for your answer: https://myboiler.com/opentherm/vaillant-opentherm/ As mentioned in the article OpenTherm protocols are implemented differently by manufacturers, so the level of OpenTherm control may vary. Hope that answer’s your question.

       Jayesh, MyBoiler Ltd

       Reply

11. Hi , I am guessing that Opentherm only works on gas boilers…Is that correct? I have an Firebird Enviromax condensing oil boiler. Regards Carmel

    Reply

    1. Hi Carmel,

       Mostly on gas boilers at the moment, there are one or two oil boiler companies with it in the works although nothing concrete as such. Here’s one such example – https://www.geniushub.co.uk/blog/genius-hub-eogb/.

       Jayesh

       Reply

       1. Thank you, for your speedy reply.

          Reply

12. Evening guys.
    I have recently fitted a Worcester greenstar 30i erp combi.
    Using combipack 4 open therm wireless thermostat.
    I have wired into live rf of boiler.
    Is this correct?
    Stat responds works fine.
    Or do I have to fit adapter to ems.
    Which I presume then fits into ot connector of receiver?
    Thanks Ian carmichael.
    If this is so.
    What is the cheapest or best option of other
    Controls?

    Reply

    1. Hi Ian,

       Yes that is correct. You would have to obtain an Opentherm to EMS adaptor for the boiler. Then connect OpenTherm Thermostat terminal to this adaptor. Please note as information is limited, the results would not be known of the performance of this setup until it is completed and tested.

       If you wish to obtain modulation without the adaptor, you would have to use Worcester Bosch’s own controls.

       Hope that helps.

       Jayesh Kanbi on Behalf of MyBoiler.com

       Reply

13. Hello, is Viessmann Vitodens 050W supported? I saw that is in comments, but I just wanted to make sure, also maybe there are some guides how to connect to it ? I was not able to find details in my manual.

    Reply

    1. Hi Arminas, It is opentherm enabled. It’s shown on page 21 of the manual under electrical connections. OT- and OT+, the connector is under the boiler. Hope that helps. Jayesh, MyBoiler

       Reply

14. Hi, I am considering installing a new Main Combi Compact or Baxi 600 same boiler I know. I would like to link it to a Honeywell T6R smart stat but read something about some stats not being compatible because of the baxi protocol is this correct
    Dsve

    Reply

    1. Hi Dave,
       Baxi doesn’t implement OpenTherm it to it’s full capability and generally leaves everything to the controller. There are some things the boiler should still have control of or at least set a maximum limit. The most compatible OpenTherm boilers are generally Viessmann, Intergas, Atag. They have a very good implementation of OpenTherm. If you are set on Baxi of which is generally a good boiler you should perhaps consider their own controller for maximum compatibility.

       Jayesh, MyBoiler Ltd

       Reply

15. The Ideal Combi pre 2016 (like mine) supports OpenTherm with a harness kit, but not OpenTherm SmartPower, so you will need either a powered thermostat or a gateway. The newer boilers support SmartPower and work with the Ideal Halo Lite wired OpenTherm thermostat. The Ideal Touch thermostat seems to have been discontinued.

    Reply

16. Good afternoon! I use a protherm bear KLOM 17 gas boiler. These adapters 0020017895 VR33 OpenTherm-Modul NL Vaillant or AWB OPENTHERM MODULE EBUS 0020092426 are compatible with my boiler for use with Nest Thermostat 3rd generation. Thanks.

    Reply

17. I have an Atag iS32 boiler which is two years old.I also have a Honeywell EVOhome system. The Atag boiler says it has an OpenTherm bus which is compatible with sone Atag products BUT I cant make it talk to my Honeywell EVO home. with the RF bridge.Atag and Honeywell have not been terribly helpful.

    Reply

    1. Hi David,

       This combination has been reported working by a few people on some forums. Provided you have gone through the correct pairing sequences and still it is not working, I would suggest possibly getting another Honeywell R8810A1018 OpenTherm bridge to compare if your current bridge is faulty. Additionally you may want to get a low cost OpenTherm programmer just to confirm the OpenTherm on the iS32 is working, although I see no reason why it shouldn’t be.

       Jayesh.

       Reply

       1. Thank you for your reply.I am on my second R8810A1018 and it is the same as the first one. What low cost OT programmer would you suggest?

          Reply

18. Hey guys,
    I’m wondering if you might shed some light for me. I can’t wrap my head around with how the OT protocol can work with Hot Water tank. Any chance you can dumb it down for me to understand how the controls work with such a setup?

    Reply

    1. Hi, as an overview on HW OpenTherm, the cylinder must be able to report it’s temperature to the OpenTherm controller and zone valves / diverting valves must be present. When hot water is being requested by the OpenTherm controller, usually it will prevent the heating zone from activating and activate the HW zone valve and send high temperature ie 80 degrees etc (unless set differently) flow water to the cylinder until it has reached it’s desired temperature. Once HW cylinder is satisfied, Heating Zone valve is free to open up again at desired flow temperatures dependent on room temp or aggregrate temps. This setup is known as priority hot water. There are other setups possible whereby the boiler is directly able to accept cylinder sensors, in this setup it’s possible to obtain a hybrid OpenTherm setup. Hope that answers your question.

       JK, MyBoiler Ltd

       Reply

19. Hi…I’m looking to upgrade the controls on my system. It’s a Vokera East-Heat 32C installed with two zone valves, controlled by 2 ESI ESRTP4RF’s. AS far as I can work out, the boiler has some sort of OpenTherm system which the ESI controllers work with. I’m concerned that a newer control, say a Drayton Wiser system (the latest version is OpenTherm) will not work with the specific Vokera OpenTherm type system. Any advice would be gratefully received!

    Many thanks

    Reply

    1. Hi in most boilers on the market today that have opentherm support, majority do not support 2 zone valves unless they are isolated and independent of the boiler ie 1 controller does the OpenTherm, 2 additional timers/programmers do the zone valves. Drayton Wiser has support for both switched live system and opentherm. So in your system setup you will not be using the OpenTherm connection of Drayton Wiser, but the switched live system using the Drayton Wiser Kit 3 (3 Channel receiver, 2 zones heating, 1 zone hot water). JK ,MyBoiler.

       Reply

       1. Thanks for such a fast and helpful response! What you’ve said makes sense and I assume it would be the same if using Tado dual channel or two nests etc. I also imagine losing OpenTherm isn’t too much of a loss.

          Can I just ask if the following is a potential solution …

          Use a single channel controller (Wiser, Tado or nest) and use it to control both the zone valves (wired together as if they were one).

          I live in England, and people seem to interpret the definition of a zone in different ways.

          Use smart radiator valves to create zones in other rooms (would be doing this in any case)

          This would potential be cheaper, and I can’t really see any advantage of having 2 zones (using valves) if most rooms are controlled by smart radiator valves.

          This solution may also allow me to use OpenTherm as well?

          Many thanks indeed.

          Chris.

          Reply

          1. Hi Chris,

             That’s pretty much correct. If you are using smart radiator valves for the entire house, then you can create virtual zones ie upstairs and downstairs seperate timings, or every room can be an individual zone, in which case you don’t need the two zone valves, you would simply latch them into the open position and dis regard the wiring completely for them, simplicity is key here. Tado and Wiser will give you OpenTherm control this way. Nest does not have any smart TRVs.

             Hope that answers your question.

             Jay.

             Reply

             1. Aha…perfect, and so simple. That is what I shall do. Thanks so much for your help.

             2. Certainly does! Thank you so much.

20. I have a Vokera Vision 25S and i am wondering if this have OpenTherm implemented. I did not found anything in the user manual. I intend to replace the existing two thermostats (cTc) with Google Nest 3rd generation. Is it worth in absence of OpenTherm? The cilinder (storage of heat water) is Joule. The existing thermostats are wired at located at ground and 2 nd floor.

    Reply

    1. Hi Victor,
       we have looked into this. Vokera Visions 25S does not have a facility for OpenTherm. It works with standard S Plan/ S Plan Plus and Y Plan wiring systems. Nest Thermostat is one choice, there are many others you may also go for and contains OpenTherm support, should you decide to change your boiler for an OpenTherm compatible one.

       Jay

       Reply

21. Hi i am going to be renovating this year and am looking to get a new boiler that is truly opentherm, i have my own opentherm gateway that i will configure up, and i wanted your opinion which boiler would be the best fit.

    Reply

    1. Hi,

       Atag, Intergas and Viessmann are among the boilers that have some of the best implementations of OpenTherm. All three have their pros and cons, that being customer support levels, engineer availability, part availability and a few more.

       Jay.

       Reply

       1. Thanks for coming back, so is the Viessmann 200-W also have opentherm support, i am seeing conflicting views on this.

          Reply

          1. Hi Vin, no it does not have OpenTherm support. I would steer you towards 100-W. The 200-W is a rolls royce of a boiler, more suited to light commercial systems. Very efficient, but long term suitability and support for a domestic home you would best stick to 100W. Jay

             Reply

             1. Ah i went on to their site and went through find me a boiler and that is what it recommended based on my requirements, also i thought it was a combi, i am looking at a system boiler as i will be putting in a separate hot water cylinder

             2. Instead of a hot water cylinder, go for the Viessman 111, We removed our cylinder after started leaking, cost of replacement along with an inefficient 18 year old system boiler and space meant it made sense. I’m in a 4 bed 70’s build house, with two baths/showers, never run out of hot water like we did with the cylinder and had hot water quickly – no waiting for the boiler to heat the hot water as with a traditional combi. Fully OpenTherm compatible, I use a Nest thermostat. saved at least 20% in gas consumption.

22. Recently connected a Viessmann Vitodens 050 up to a Tado stat on opentherm and seems to be working well also. Instructions are not very clear and require D01 stat setting rather than the D37 Viessman specific settings on the Tado

    Reply

    1. Hi Chris, thanks for your findings. The reason for this is that the Viessmann has a multi connector that is able to be reconfigured digitally. I am assuming you have the newer 050, the one with remote monitoring capability. Jay.

       Reply

23. Hello,
    I have a Bulex IsoTwin Condens 25/31 https://www.bulex.be/particuliers/produits/isotwin-condens-85632.html
    for which Bulex advised that the AWB 0020092426 module is compatible.
    But i have seen that the OpenTherm version on this module is 2.3, whereas i want to connect it to a Bosch/Nefit CT200, through an Bosch/Nefit EasyAdapter – which uses OpenTherm 4.0.
    Whereas OpenTherm should be backwards compatible, i wonder if anyone has tried this already and if it works.
    Or – is there a posibility to update the firmware of this device?
    Thank you.

    Reply

24. Hi – great set of articles here, but I’m still stuck on 1 aspect:

    Currently looking at getting a new combi (specifically Intergas Xclusive or Atag IC Economiser), is there still any benefit in getting one which has OpenTherm?

    Reply

    1. Hi Mal,
       The Intergas and Atag are both very top class boilers in terms of efficiency, and both support OpenTherm as standard. There is advantage in getting OpenTherm versus non OpenTherm, however it’s more important to make sure you have modulating heating controls. So for Vaillant you would go with Ebus controls ie their own range. For the likes of Intergas, Viessmann, Atag and a few others you can go with OpenTherm such as Nest / Drayton (OpenTherm), Honeywell (OpenTherm) etc or you can go with their own proprietary controls with provide a bit more control and information. Hope that answers your questions. Jay.

       Reply

25. So disappointing that the Worcester has so few boilers with OpenTherm, a highly rated expensive boiler with no modern energy efficient controls! That and no stainless-steel heat exchanger (I live in a hard water area with a water softener) made for my decision to go with a Viessmann.

    Reply

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