OpenTherm Boilers and Controls

OpenTherm Logo
OpenTherm Logo

Shown below are a list of OpenTherm capable / compatible manufacturers and boilers. These OpenTherm Boilers / OpenTherm capable boilers have integrated OpenTherm unless specified otherwise in brackets. For more info on “What is OpenTherm?” at the  OpenTherm Association. You can also see our OpenTherm Capable Controls shown further down the page.

For homeowners: what OpenTherm means see the following page: Modulating ‘A Rated’ Boilers with Smart Modulating Thermostats

What is OpenTherm?

Wikipedia: OpenTherm (OT) is a standard communications protocol used in central heating systems for the communication between a central heating boiler and a thermostatic controller. A two way communications interface, usually in the form of a slave and master device.

As a standard, OpenTherm is independent of any single manufacturer. A controller from manufacturer A can in principle be used to control a boiler from manufacturer B. However, OpenTherm controllers and boilers do not in fact always work properly together. The OpenTherm standard comprises a number of optional features and some devices may include manufacturer-specific features. The presence or absence of such features may impair compatibility with other OpenTherm devices.

OpenTherm History?

OpenTherm was originally created by Honeywell and was sold to the OpenTherm Association on November 1996 for one British Pound. This was no doubt to make the standard independent of any manufacturer.

Modulating Control

Unlike room thermostats that simply tell the boiler when to turn on and off (non modulating graph below) , a modulating control (see modulating graph below) tells the boiler the exact target / set point temperature that is required to be achieved. So as the current temperature starts getting closer to the set point temperature, the boiler starts reducing the flow temperature to match the required demand.

Non modulating thermostat

Image Above: Standard On-Off type boiler / controls

Modulating Thermostat Graph

Image Above: OpenTherm / Modulating boiler with modulating controls.

OpenTherm Advanced setups

OpenTherm is easier to use on combi boilers, the reason is that there is no hot water cylinder to control. Stored hot water requires heating to the correct temperatures as required by legionella prevention(recommended 60 degrees), as OpenTherm can reduce flow temperatures to below 60 degrees. So, on system and regular boilers that have opentherm, in order to also work with hot water cylinders, cylinder temperature reporting must be present in some form. This allows the OpenTherm to fire at high temperature just for the hot water. Note, is is advised that in this setup there is priority to the hot water system, otherwise higher temperatures may reach the radiators when you don’t want them to.

OpenTherm Compatible Boilers

For Manufacturers: If your boiler model is not in this list, please contact us via our contact form or via twitter for any additional information

Vaillant Ecotec 4XX Series requires additional steps. Please see following thread:

BrandModelAdditional InfoFuelLink
alpha logoAlpha Heating Innovation
BrandModelsAdditional InfoFuelUrls
Alpha HeatingE-Tec SNG
Alpha HeatingE-tec PlusNG
Alpha HeatingE-tecNG
Alpha HeatingEvokeNG
Alpha HeatingIntec GSNG

Atag Heating Technology
BrandModelsAdditional InfoFuelUrls
AtagiC EconomiserNG

BrandModelsAdditional InfoFuelUrls
Baxi100 CombiOpenTherm is Terminals 1 and 2 on the M2 Low Voltage Terminal BlockNG
Baxi200 CombiOpen Therm connecter is labelled 'Bus'NG
Baxi400 CombiOpen Therm connecter is labelled 'Bus'NG
Baxi600 CombiOpen Therm connecter is labelled 'Bus'NG
Baxi600 SystemOpen Therm connecter is labelled 'Low Voltage Controls'NG
Baxi800 Combi - 825 830 836NG

BrandModelsAdditional InfoFuelUrls
DaikinD2CND 24KwCombi BoilerNG
DaikinD2CND 28kwCombi BoilerNG
DaikinD2CND 35kwCombi BoilerNG

BrandModelsAdditional InfoFuelUrls
EOGBSapphire 23kW6-23kW ModulationOil (HVO & Kerosene)Link
EOGBSapphire 28kW6-28kW ModulationOil (HVO & Kerosene)Link
EOGBSapphire 32kW6-32kW ModulationOil (HVO & Kerosene)Link

BrandModelsAdditional InfoFuelUrls
FiammaCombi Elektra Compact 12C, 18C, 24C12KW, 18KW, 24KWElectric

ModelsAdditional InfoFuelUrls
Ferrolii25, i29 Condensing Combination BoilerNG
FerroliBluehelix Tech RRT 24C, 28C, 34C Condensing Combi Boiler NG
FerroliBluehelix Tech RRT 18S, 28S, 30S Condensing Combi Boiler NG

Ideal Boilers
BrandModelsAdditional InfoFuelUrls
IdealIndependent + CombiOption Kit may be requiredNG
IdealIndependent CombiOption Kit may be requiredNG
IdealIndependent SystemOption Kit may be requiredNG
IdealLogic Combi+ Combi CNG
IdealLogic Combi C24, C30, C35 Requires seperate harness kitNG
IdealLogic Code CombiRequires seperate harness kitNG
IdealI-mini C24, c30 Requires seperate harness kitNG
IdealVogue Combi C26,C32, C40NG
IdealLogic + System(Works with Evohome)NG
IdealLogic + Heat(Works with Evohome)NG
IdealLogic Combi ESP1 24, 30 , 35NG

ideal commercial logoIdeal Commercial
BrandModelsAdditional InfoFuelUrls
Ideal CommercialEvomaxNG
Ideal CommercialImaxNG

Intergas Boilers
BrandModelsAdditional InfoFuelUrls
IntergasIntergas RapidNG
IntergasIntergas Rapid PlusNG
IntergasCombi CompactNG
IntergasCompact RangeNG
IntergasECO RFNG
IntergasXtremeDual OpenThermNG
IntergasXclusiveDual OpenThermNG

keston logoKeston
BrandModelsAdditional InfoFuelUrls
KestonCombi C30 & C35Requires seperate harness kitNG
KestonSystem S30NG
KestonHeat 45 and 55NG

Main Heating logo Red RGBMain
BrandModelsAdditional InfoFuelUrls
MainEco Compact Combi 25-30Same accessories as Baxi.NG

KD Navien
BrandModelsAdditional InfoFuelUrls
NavienNCB300Natural Gas / LPG
NavienNCB500 OnNatural Gas / LPG
NavienNCB700 OnNatural Gas / LPG
NavienLCB700 OilOil

BrandModelsAdditional InfoFuelUrls
RavenheatHE30S CompactNG
RavenheatHE98S CombiNG

Remeha Boilers
BrandModelsAdditional InfoFuelUrls
RemehaQuinta AceNG
RemehaQuinta ProNG
RemehaGas 110 EcoCommercialNG

BrandModelsAdditional InfoFuelUrls
TepeoZEB-40SSystem BoilerElectric
TepeoZEB-40RRegular BoilerElectric

BrandModelsAdditional InfoFuelUrls
ViessmannVitodens 100W Type WB1A (Connection: X3.3 and X3.4)NG
ViessmannVitodens 100W Type WB1B (Connection: X21.1 and X21.2)NG
ViessmannVitodens 100W Type WB1C (Connection: X21.1 and X21.2)NG
ViessmannVitodens 100W Type B1HA, B1KA
(Connection: X21.1 and X21.2)
ViessmannVitodens 200-W WB2B 26+ 35 kW (via Expansion Module OT and OT-A8 + _Terminal -10 and +10 are on expansion A8 boiler )NG
ViessmannVitodens 200-W WB2C, B2HA,B2JA, B2LA (via icm Expander OpenTherm)NG

BrandModelsAdditional InfoFuelUrls
VokeraEvolve CNG
VokeraEvolve SNG
VokeraLinea One (via OpenTherm Kit Part_1221179)NG
VokeraVision Combi (requires control interface 29450143)NG
VokeraCompact A (requires control interface 29450143)NG
VokeraVerve_(heating only mode)NG
VokeraMynute i (heating only mode)NG
VokeraUnica iNG
VokeraVibeSystem boilerNG
VokeraVision CNG
VokeraLinea HENG
VokeraMynute ASystem boilerNG
VokeraMynute HENG
VokeraUnica HENG

Opentherm Compatible Boilers List Last Updated: 26/09/2022

OpenTherm Compatible Boilers – Unofficially Compatible

The following boiler models, mostly Vaillant and Worcester Bosch are capable unofficially. Using the mentioned adaptors may invalidate your warranty. However boilers that are out of warranty will have no known problems, as these adaptors are purpose made by the companies themselves for some European countries, where governments have made it compulsory to have OpenTherm.

BrandModelAdditional Info

BrandModelsAdditional Info
VaillantEcotec Pro [1]
VaillantEcotec Plus_[1][2]
VaillantEcotec Exclusive[1]
VaillantEcofit Pure_[1]
[1] Using un-official VR33 Module Vaillant OpenTherm and VR33
[2] Ecotec 4XX Series requires additional steps.

Glow Worm
BrandModelsAdditional Info
Glow-WormBetacom 1,2,3,4Requires Adaptor
Glow-WormEasicom 1, 2, 3Requires Adaptor
Glow-WormEnergy 35 StoreRequires Adaptor
Glow-WormEnergy CombiRequires Adaptor
Glow-WormEssentialRequires Adaptor
Glow-WormFlexicomRequires Adaptor
Glow-WormUtracomRequires Adaptor
Glow-WormUltimate3Requires Adaptor

Worcester Bosch
BrandModelsAdditional Info
Worcester BoschEMS capable boilers [1]Worcester Bosch and OpenTherm Page
Worcester BoschGreenstar i [1]Requires Adaptor
Worcester BoschGreenstar i Junior [1][**]Requires Adaptor
Worcester BoschGreenstar Si Compact [1]Requires Adaptor
Worcester BoschGreenstar CDi Compact [1]Requires Adaptor
Worcester BoschGreenstar CDi Classic [1]ŒŠí_í_]Requires Adaptor
Worcester BoschGreenstar Highflow CDi [1]Requires Adaptor
Worcester BoschGreenstar 12i System - 24i System [1][*^]Requires Adaptor
Worcester BoschGreenstar 27i System - 30i System [1][*]Requires Adaptor
Worcester BoschGreenstar CDi Classic System [1][*ŒŠí_í_]Requires Adaptor
Worcester BoschNote: Worcester Bosch OpenTherm information is very limited, please accept this list as capable, but not yet confirmed. There is also no confirmation of hot water working with OpenTherm
[1] Using un-official Nefit Adaptor
[*] Provided optional integral diverter valve is installed
[**] Manufactured after July 2013
[ŒŠí_í_] Manufactured after 16th January 2007 with software version CF12.10 onwards.
[^] Manufactured after February 2011.

Opentherm Compatible Boilers List Last Updated: 24/11/2018

OpenTherm Compatible Controls

Following are a list of OpenTherm compatible controls. These controls are compatible with Open Therm Capable boilers shown above. Smart Thermostats are listed first. Where an addition tranceiver is required it will be specificied in the brackets. See more info on OpenTherm at the OpenTherm Association.For homeowners: what OpenTherm means see the following post: What is OpenTherm?

Open Therm fact sheet from Honeywell the original creators of OpenTherm:   OpenTherm Fact Sheet

BrandModelReview Page / Info page.Wired / WirelessRadiator ValvesInternet ConnectedHomekitOther
Baxi uSense smart room thermostatNY
Delta DoreTybox Bus OT - 6053056WiredNNN
DraytonWiser Kit 1WirelessYYNHeating Only
DraytonWiser Kit 2WirelessYYNHeating and Hot Water
DraytonWiser Kit 3WirelessYYN3 Zone Support
DraytonDigistat 2290MWiredNN N(Bluetooth App)
DraytonDigistat RF901WiredNN N(Bluetooth App)
EPH ControlsCP4BWired (Batteries)NN
EPH ControlsCP4MWired(No Batteries Required)N
(Combi Pack 4)
WirelessN1 Zone
EPH ControlsCP4-HW-OTWirelessN
EPH ControlsCP4iWirelessY
EsiESRTP4OT Programmable Room ThermostatWiredNNN
EsiESRTP4RF+ Programmable Room ThermostatWirelessNNN
HeatmiserneoHub Mini with NeoAirWirelessNY(with NeoHub) 2 Zones with OpenTherm capable
HoneywellT4MWiredNNNoptional WC curve setting and internal reference - no support for DHW setpoint.
Honeywell T4RWirelessNNNno support for DHW setpoint.
HoneywellLyric T6WiredYYYsupport for DHW setpoint and overnight preheat disable for combi boiler applications.
HoneywellLyric T6RWirelessYYYSupport for DHW setpoint and overnight preheat disable for combi boiler applications.
HoneywellT6R-HWWirelessYYYSupport for DHW setpoint and overnight preheat disable, plus timed hot water control for storage combis and system boilers.
HoneywellEvohomeWirelessYYNRequires R8810
HoneywellCM727WirelessNNNRequired R8810
HoneywellCMS927B1049 Room UnitWirelessNNNRequires R8810
IdealLogic RF7WirelessNNN
IdealTouch Connect Wifi Combi Control 214217
NestSmart Thermostat 3rd GenerationWirelessNYN
NestSmart Thermostat E 3rd GenerationProduct InfoWirelessNYN
RemehaiSenseWired / WirelessNNN
TadoTado Smart Wired ThermostatWiredYYY
TadoTado Wireless Extension KitWirelessYYYTado Wireless Extension Kit with receiver (BR02/ BU02) starting serial number BR/BU* has an Analog/Digital Interface including OpenTherm Support, Ebus.
Vokera20050690 Open Therm 7 Day Programmable RF Room ThermostatWiredNNN
VokeraOpenTherm RF Programmer (20050690)WirelessNNN
Last Updated: 25/09/22
OpenTherm Compatible Controls Last Updated: 10/12/2019


Credits/ Sources / Public Contributors:

Richard Huish

Automatedhome; HenGus, Bruce_Miranda

Steve Todd

John Lockwood

Patrick McMahon

Information Sources: 

Page Content Last Updated: 26/09/2022

101 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.
    Paul Cracknell

    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


  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.

    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

  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?

    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.

      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.

        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

    1. Hi, Thank you Patrick.

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


      Jayesh Kanbi

  4. 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,
    George Arnautu

  5. 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.

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

    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 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.

  7. 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?

  8. 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

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

  10. 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

    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

  11. 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.

    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

  12. 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

    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

  13. 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.

  14. 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.

  15. 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.

    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.


      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?

  16. 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?

    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

  17. 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

    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.

      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.


        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.


          1. You can effectively use any smart TRV system with Nest, the only thing is that Nest has no direct control of the TRVs, the control is only via cloud integration. Ie if the TRV cloud connection breaks, then the TRVs would not be able to tell the Nest Thermostat to come on/ off.

  18. 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.

    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.


  19. 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.

    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.


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

        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

          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.

  20. 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

    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.

  21. Hello,
    I have a Bulex IsoTwin Condens 25/31
    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.

  22. 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?

    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.

  23. 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.

  24. We have Honeywell Evohome with several zones and we have just replaced our elderly boiler with a Baxi 600 combi (Main Eco Compact) as it was our understanding this boiler is Opentherm compatible. Now this is true when the boiler is connected to Baxi’s own iSense controller as Baxi boilers deactivate the flow controls when running Opentherm and default to DCH 80c and DHW 60c. The iSense provides flow control, so these defaults are overridden, but most controllers, including Evohome, don’t offer any flow controls, so you’re left with whatever the boiler defaults to.

    Of course, none of this is explained on the Baxi website, so now we are left with an incompatible Opentherm setup as we have no control over DHW with 60c at the taps being far too hot and the boiler running up to a maximum of 80c, which is incredibly inefficient when we would have ideally set the DCH flow to a maximum of 50c.

    Other than ditching Opentherm and moving to a Baxi IFOS weather optimisation, do you have any ideas or workarounds? I have read of temporarily binding a Honeywell Opentherm controller with flow controls to the bridge, setting DCH and DHW temperatures, which are then transferred to the boiler, and then rebind to Evohome. Less than ideal as it’s a lot of hassle if you need to then adjust flow temperatures with changing seasons plus I haven’t identified the Honeywell Opentherm controller with the all important flow controls.

    Incredibly disappointed with Baxi’s interpretation of Opentherm and its decision to deactivate flow controls when running this protocol.

    1. Hi Stef,

      Unfortunately you have now witnessed the issue with the boiler industry even though standards exist. Not all manufacturer’s implement the OpenTherm standard correctly. The only work around we have used in the past is to use the manufacturer’s controls to gain maximum efficiency and simply make Honeywell Evohome system a passive system that is not able to command the boiler, only able to regulate the individual rooms passively either in standalone mode or still connected to the app.

      Weather compensation in our experience offers the highest levels of efficiency versus Room Sensor based operation. When you have weather compensation, usually you don’t need individual room control, as a well set weather curve ensures high efficiency and comfort levels throughout the home.

      Hope that helps.

      Jayesh Kanbi

      1. Hi Jayesh,

        Thank you very much for the detailed reply. We purchased the Baxi IFOS weather compensation for under £30, sold the R8810 Opentherm relay, reinstalled the Honeywell BDR91 relay and it’s now all running very well indeed over 8 x HR92 controlled zones, which will become 11 when we have finished work on the house.

        You are not the first person to suggest weather compensation is the more efficient option, so Baxi”s poor interpretation of Opentherm did us a favour.

        Thanks again for your reply and advice.

  25. Hi I have an Alpha Intec 34c, I was wondering if they are OpenTherm compatible? And if the kw on the heating side can be rated down? Thanks

    1. Hi Steve,

      It does not support OpenTherm, and unfortunately does not support range rating of the output. The newer Alphas do support both functions. The best thing you can do is to reduce your flow temperature where possible to maximum 55 degrees for majority of the year. see this article for more info to save on energy. , additionally it may help to have smart controlled TRVs such as Tado or Drayton. Hope that helps.

  26. We have a Worcester Greenstar 40CDi boiler and wish to install a full Drayton Wiser control system with 12 zones and TRV’s on all radiators. The Drayton Wiser kit comes with a “Heat Hub” and a “OpenTherm Module” amongst other things.

    Your review says that the boiler supports OpenTherm with additional of an “unofficial Netfit Adaptor”. Is this adaptor the same as the “OpenTherm Module” which comes with the Wiser or are they different things?
    If they are different things, where can I source the “unofficial Netfit Adaptor”?

    Many thanks

    1. Hi Chris,

      We aren’t able to provide any further information on the adaptor other than what’s on the article. The information in the article is provided by external contributors.

      Please note the Adaptor is for the boiler, it is not provided with the Wiser kit, that is simply referring to the built in OpenTherm interface ie it is able to control an OpenTherm capable boiler. It is not capable of controller other bus enabled boilers.

      Hope that helps.

      Jayesh Kanbi

  27. Hi,

    Excellent forum that’s really well supported. I have a Vaillant Home regular 25 that was fixed in our new build home that we moved in to 4 years ago. I have Hive fitted on it and realize that Hive doesn’t make things efficient if I am to interpret this article in relation to our situation.

    I am thinking of of a wholesale change to our system with a Mixergy Hot water tank and a suitable boiler and good controls. How can I find more information to get the best possible solution / deal for this and do you think such a big change will save investment that in the medium term (4-5 years)?

    1. Hi,

      Just consider keeping the Vaillant Home boiler and consider an upgrade to using either the full Vaillant controls/ or hybrid solution of Vaillant junction wiring centers with Tado remote controller to control the setup. Vaillant controls will provide maximum efficiency. Although you may need to consider speaking with Mixergy technical for the integration of the Vaillant controls with the cylinder.


    2. Hi

      Also to add, as it is a new build see if it will support a heat pump without too much alterations. You can also apply for a BUS grant for replacing your boiler.


  28. Hi, I have a 10 year old Worcester system boiler and am going to change it for a Navien NCB-28LDWE combi wihich says it has Open Therm compatibility. Rather than the EPH Combipack 4 controls can I use a Tado V3+ thermostat with this and still get Open Therm benefits?

    1. Hi Stuart,

      Absolutely. However you must get the Tado Wired receiver as that definitely contains OpenTherm, or you must order the Wireless receiver direct from Tado that contains OpenTherm. The OpenTherm V3+ Wireless kit in the UK does not contain OpenTherm. The Wired V3+ kit does contain OpenTherm.

      Please let us know how the Navien boiler is, it’s one of a small handful of boilers, we have not installed to date.


  29. Hi Jayesh, Thanks very much for the speedy reply. I was looking at the wireless version for simplicity but will contact Tado directly re OpenTherm issue. I did get an even quicker response from them today and they specifically asked if we were in the UK…now I know why.. but seemed more interested in the model number of the EPH Combipack receiver for some reason. Still awaiting their update. Will let you know re the Navien.
    Thanks again.

    1. Hi,

      I have a Glowworm Ultracom 24 hxi boiler, on your unofficial list, you have Glowworm Ultracom boilers as needing an adaptor. Can you explain what adaptor and anything else required to make the boiler talk opentherm?


      1. Hi Richard,

        Please read the entire article and you will find an answer. We cannot provide direct advice to individuals unless you are sufficiently competent to work with gas boilers and electronics. However as a simple explanation, you need an OpenTherm Interface suited to your boiler and a OpenTherm capable Heating control / Thermostat. I hope that gives you enough information to begin your OpenTherm journey.

        Jayesh Kanbi.

  30. Hello , i have an IMMERGAS VITRIX 26kw gas boiler , i found nowhere in the manual or in the Internet if it supports OpenThem. My boiler in combination with an IMMERGAS thermostat called Car V2 informs me regarding errors etc, could you please confirm to me that it is OpenTherm compatible?

        1. Hi,

          Nothing in the installation and servicing manuals indicate that it is OpenTherm compatible. Although it does have some form of Bus connection it defenitely does not appear to indicate OpenTherm. Hope that helps.


  31. HI I now buy new Remeha Ace 24C I think it is compatible OpenTherm. I have Honeywell Evohome ATC928WIFI and 8 zones there are HR92. Old boiler On/Off BDR91 and now only needed HONEYWELL R88 OPENTHERM? thanks

        1. Hi,
          If that is your version, then clearly is does state OpenTherm capability. Most dutch boilers contain OpenTherm as mandated by their government. The connector X6, Terminal 3 and 4 appear to be the OpenTherm connections.

          1. Hi,
            As long as your boiler is the same as the Dutch one then it is ok. If the Hungary version is with a different connector or without OpenTherm then it won’t work. Most likely it makes sense to use the same PCB, there is no reason for Remeha to remove it from the PCB just for the Hungarian version, although you never know. JK

  32. I have a Baxi 630 combi with a Usense Open Therm control.
    It appears that its not possible to lower the boier flow temperature with this set, just the max and min outputs on the boiler.
    The manual says it defaults flow temperature to 80 degrees but this seems to be at odds with the latest part L regs with flow temps needing to be 55 degrees?
    Is there a way of lowering the flow temp?

    1. Hi,

      Sorry this comment got held in the queue. The baxi implementation of OpenTherm is not great at all. To guarantee low flow you would be best with standard controls and setting to 55-60 degree flow temp. The lower the better. Viessmann, Intergas, Atag and some others generally have the best OpenTherm implementation.


  33. The Viessmann 200-W combi seems to be not opentherm capable whereas the 100-W is. Their top model only offers weather compensation which is strange when the lower models offer both. Is there anyway to make the 200-W opentherm capable?

    1. Hi Chris,

      The Viessmann 200-W is a highly advanced boiler that on the latest model used PlusBus controls. It does not actually require OpenTherm to perform well. You should use Weather Compensation and switched live controls etc. I would highly recommend for you to contact a local Viessmann specialist and go through the options with them, alternatively you may try technical. This boiler really has maximum benefit, when you have minimum amount of controls and restriction etc. There may be an adaptor out there. Being Viessmann specialists, we would recommend for this particular boiler to use as much of Viessmann’s own controls as possible.

      1. Is there a list of boilers which can run opentherm and have been known to work with the Drayton Wiser controller? An owner has said in an online forum, that a Viessmann 100 boiler (2022 year) does not work with a Wiser controller using opentherm, even though both are stated as being able to use it.

        Is opentherm faster at warming a cold room using a smart TRV (Wiser) than weather compensation due to the CH water varying over the time needed to heat the room? My assumption is that weather comp would use a lower water temp to match the heat loss to the outside, and would require longer to get to the required temperature of the room.


        1. Hi,
          OpenTherm will always be faster for a cold room as immediately goes at high flow temp. Whereas a weather controlled temp will always vary temperature at flow temp to suit the weather. OpenTherm can be made to go at high flow temp simply by increasing the target temperature higher than normal and putting it back as you get closer to desired temp. Weather compensated generally creates more comfortable temperatures within the house as it’s not using an accurate reference point at determined by the location of the OpenTherm thermostat. Pros and Cons for both. Our preference after extensive testing is Weather Compensation.

  34. Hey, thanks for the great article that helped me a lot (mostly the discussion below), but I’m still not sure about some things as I’m currently switching my 22y old Vitodens 200 WB2 for a (most probably) new 100-W B1HF.
    I’m also aiming for a smart modulating OpenTherm thermostat in a living room (that has “in-floor” radiators that can’t be operated by smart TRVs) + smart TRVs in other rooms that are compatible with HomeKit. Mostly because i wanna control separate rooms based on presence of certain people that isn’t really on a strict schedule (irregular workdays, lots of “away” days etc) and it seems to work best in HomeKit even though I’ve got HomeAssistant set up at home. Do you have any experience with both Tado V3 and Netatmo (the new modulating OT thermostat) and can recommend which ecosystem would work better with the new Vitodens 100-W? From what i’ve read Tado is a bit less user-friendly to install but once set up it’s working very well, whereas Netatmo seems to be temperamental and sometimes just refuses to work (Legrand being french maybe? 😉 ). Also the Tado TRVs seem to be quieter and less problematic than those from Netatmo. I also considered the ViCare TRVs and thermostats but they’re overpriced for what they offer and no way to correlate rooms to people at home even through HomeAssistant’s ViCare integration from what i know.

    1. Hi Konrad,

      The 200-W is an excellent boiler with ultra low modulation capability. However you must try to use as much of Viessmann controls as possible for maximum benefit. Ideally the less controls the better ie treating each floor as 1 zone rather than micro zoning. You will achieve excellent efficiency with minimal components.This works best when the home is more insulated and not so leaky.

      If you go down the 100-W route that has OpenTherm capability, then the overall smart system winner is Tado. We have done extensive research and have first hand experience. Tado is also able to control the infloor underfloor heating too. Tado has some minor issues ie being cloud based, apart from that, the quality of it overall including the user interface and integrations, beat the rest hands down. It’s also compatible with Home Assistant. Tado’s TRVs are able to regulate temperature to a fine degree and have variable levels ie from 0% to 100% open. Tado uses linear motors and are relatively quiet as it uses very quick movements.

      Sometimes the French don’t play with the Brits :-), but some of there manufacturing still beats UK in terms of quality. I believe the ViCare TRVs might be rebranded Danfoss valves, although at one point im sure they were using Tado valves. No info for the UK on those valves as Tado has become the clear leader.

      Hope that help.

  35. Hi, I am running a Worcester Bosch 8000 life regular boiler with a hot water tank, and have fitted the netfit Open therm converter (7 746 900 496). It is linked to Nest smart thermostat on the open therm setting. How can i tell that it is working, the nest says that it has found the open therm. The boiler is working, I guess i am looking for the boiler to modulate down as the stat approaches its target temp. Haven’t seen that yet. Wondered if this set up will work with this boiler?

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