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 for this is that there is no hot water cylinder to worry about, heating to the correct temperatures as required by legionalla prevention(recommended 60 degrees), as OpenTherm can reduce flow temperatures to below 60 degress. 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 twitterAdditional Information

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

BrandModelAdditional Info
alpha logoAlpha Heating Innovation
BrandModelsAdditional Info
Alpha HeatingE-Tec S
Alpha HeatingE-tec Plus
Alpha HeatingE-tec
Alpha HeatingEvoke
Alpha HeatingIntec GS

Atag Heating Technology
BrandModelsAdditional Info
AtagiC Economiser

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

BrandModelsAdditional Info
DaikinD2CND 24KwCombi Boiler
DaikinD2CND 28kwCombi Boiler
DaikinD2CND 35kwCombi Boiler

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

Ideal Boilers
BrandModelsAdditional Info
IdealIndependent + CombiOption Kit may be required
IdealIndependent CombiOption Kit may be required
IdealIndependent SystemOption Kit may be required
IdealLogic Combi+ Combi C
IdealLogic Combi C24, C30, C35 Requires seperate harness kit
IdealLogic Code CombiRequires seperate harness kit
IdealI-mini C24, c30 Requires seperate harness kit
IdealVogue Combi C26,C32, C40
IdealLogic + System(Works with Evohome)
IdealLogic + Heat(Works with Evohome)
IdealLogic Combi ESP1 24, 30 , 35

ideal commercial logoIdeal Commercial
BrandModelsAdditional Info
Ideal CommercialEvomax
Ideal CommercialImax

Intergas Boilers
BrandModelsAdditional Info
IntergasIntergas Rapid
IntergasIntergas Rapid Plus
IntergasCombi Compact
IntergasCompact Range
IntergasECO RF
IntergasXtremeDual OpenTherm
IntergasXclusiveDual OpenTherm

keston logoKeston
BrandModelsAdditional Info
KestonCombi C30 & C35Requires seperate harness kit
KestonSystem S30
KestonHeat 45 and 55

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

KD Navien
BrandModelsAdditional Info
Navien NCB
Navien LCB700 Oil

BrandModelsAdditional Info
RavenheatHE30S Compact
RavenheatHE98S Combi

Remeha Boilers
BrandModelsAdditional Info
RemehaQuinta Ace
RemehaQuinta Pro
RemehaGas 110 EcoCommercial

BrandModelsAdditional Info
ViessmannVitodens 100W Type WB1A (Connection: X3.3 and X3.4)
ViessmannVitodens 100W Type WB1B (Connection: X21.1 and X21.2)
ViessmannVitodens 100W Type WB1C (Connection: X21.1 and X21.2)
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 )
ViessmannVitodens 200-W WB2C, B2HA,B2JA, B2LA (via icm Expander OpenTherm)

BrandModelsAdditional Info
VokeraEvolve C
VokeraEvolve S
VokeraLinea One (via OpenTherm Kit Part_1221179)
VokeraVision Combi (requires control interface 29450143)
VokeraCompact A (requires control interface 29450143)
VokeraVerve_(heating only mode)
VokeraMynute i (heating only mode)
VokeraVision System (heating only mode)
VokeraUnica i
VokeraVibeSystem boiler
VokeraVision C
VokeraLinea HE
VokeraMynute ASystem boiler
VokeraMynute HE
VokeraUnica HE

Opentherm Compatible Boilers List Last Updated: 02/09/2019

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 ThermostatWired / WirelessYYYRequires Extension Kit
Vokera20050690 Open Therm 7 Day Programmable RF Room ThermostatWiredNNN
VokeraOpenTherm RF Programmer (20050690)WirelessNNN
Last Updated: 27/05/21
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 Last Updated: 04/04/2019

41 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. 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.


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