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Thread: Evohome replace existing dial thermostat

  1. #11
    Automated Home Sr Member electronicsuk's Avatar
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    Quote Originally Posted by jonboy View Post
    The condensing boiler is a Viessmann Vitodens 100W. I note that Viessmann produce Open Therm compatible boilers, but I would have to check if my specific model comes into this category. Can you please explain how I can discard the BDR91 and how this would be more efficient? If it was possible to dispense with the BDR91 does this mean a more complicated installation procedure?
    Honeywell are a bit light on the details when it comes to the OpenTherm bridge, but the general premise behind OpenTherm is that it hands a lot more control of the boiler over to the thermostat. Rather than simply turning the boiler on or off, the thermostat can modulate flow temperatures and such, keeping the boiler in condensing mode for as long as possible and thereby increasing the efficiency of the system. Exactly how much of a difference this all makes I have yet to tell, but I am using the OpenTherm bridge on my system. Installation is very simple, just two wires to connect to the boiler.

    Quote Originally Posted by jonboy View Post
    The Danfoss wall thermostat in the hall is fitted to a plastic wall box so can I assume that this would be a straightforward installation by simply connecting to the existing 240V cable?
    If there's a continuous supply there then yes, it should be pretty easy. If not, you may need to make some changes to the wiring at the other end. You'll also want to get the wall-mount kit for the EvoHome controller.

    Quote Originally Posted by jonboy View Post
    If the BDR91 is utilised I assume it can be simply substituted for the controller with the appropriate wires swopped over, or is it more complex than this?
    Shouldn't be much more to it than that, especially as you don't need to worry about hot water control.

  2. #12
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    Thanks for your reply electronicsuk.

    When you say "the thermostat can modulate flow temperatures" do you mean each individual radiator thermostat?

    You say "Installation is very simple, just two wires to connect to the boiler". Can you please elaborate? Where do the wires come from if there is no BDR91? Can you refer me to instructions on how to do this?

  3. #13
    Site Sponsor The EVOHOME Shop's Avatar
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    Quote Originally Posted by jonboy View Post
    Thanks for your reply electronicsuk.

    When you say "the thermostat can modulate flow temperatures" do you mean each individual radiator thermostat?

    You say "Installation is very simple, just two wires to connect to the boiler". Can you please elaborate? Where do the wires come from if there is no BDR91? Can you refer me to instructions on how to do this?
    OpenTherm was developed by Honeywell and basically allows the evohome system to adjust an OpenTherm compatible boilers heat output based on the heating demand requirements of the evohome system.

    The R8810 OpenTherm Bridge has two terminals and you basically use low voltage wires that attach the OT Bridge to the two OpenTherm terminals on the boiler. The boilers OpenTherm connection will power the R8810 OpenTherm Bridge.

    Bear in mind there is specific system design criterion for 'system boilers' using OpenTherm with evohome - no motorised zone valve on heating side of the system and HR92's fitted to all radiators is one such requirement. Combi boilers are simpler, but if you have motorised zone valves fitted for a two zone heating system the previous statement applies also.

  4. #14
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    Quote Originally Posted by The EVOHOME Shop View Post
    OpenTherm was developed by Honeywell and basically allows the evohome system to adjust an OpenTherm compatible boilers heat output based on the heating demand requirements of the evohome system.

    The R8810 OpenTherm Bridge has two terminals and you basically use low voltage wires that attach the OT Bridge to the two OpenTherm terminals on the boiler. The boilers OpenTherm connection will power the R8810 OpenTherm Bridge.

    Bear in mind there is specific system design criterion for 'system boilers' using OpenTherm with evohome - no motorised zone valve on heating side of the system and HR92's fitted to all radiators is one such requirement. Combi boilers are simpler, but if you have motorised zone valves fitted for a two zone heating system the previous statement applies also.
    Thank you for your reply.

    It would appear that our Viessmann Vitoden 100-W is Opentherm capable as the company produces the Vitotrol 100 open therm controller for use with the boiler.

    It is a new combination boiler with no motorised zone valves as far as I am aware. Hot water is on demand with no storage system.

    Is there a significant benefit to installing the R8810 rather than the BDR91?

    Can R8810 be more or less problematic once installed?

    Is the R8810 easier to install?

    Can the Evohome controller be purchased more cost effectively as a stand alone unit?

    I am still trying to get a handle on all this.

  5. #15
    Automated Home Legend top brake's Avatar
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    Quote Originally Posted by jonboy View Post
    Thank you for your reply.

    It would appear that our Viessmann Vitoden 100-W is Opentherm capable as the company produces the Vitotrol 100 open therm controller for use with the boiler.

    It is a new combination boiler with no motorised zone valves as far as I am aware. Hot water is on demand with no storage system.

    Is there a significant benefit to installing the R8810 rather than the BDR91?

    Can R8810 be more or less problematic once installed?

    Is the R8810 easier to install?

    Can the Evohome controller be purchased more cost effectively as a stand alone unit?

    I am still trying to get a handle on all this.
    using the R8810A1018 will allow the boiler to modulate rather than being switch 0 or 100% using TPI on a cycle/minimum run time basis

    the benefits of modulating the boiler include lower gas use, more efficient operation and closer more stable control

    R8810A1018 is powered from the OpenTherm terminals on the boiler so no mains supply needed

    regarding purchasing all the parts are available separately so if you don't need a BDR91 to control boiler you can buy the (spare) controller, R8810A1018 and either desk or wall mount

    parts list on back of brochure
    http://www.honeywelluk.com/Documents...20approved.pdf
    Last edited by top brake; 16th October 2015 at 11:49 AM.
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  6. #16
    Site Sponsor The EVOHOME Shop's Avatar
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    Quote Originally Posted by top brake View Post
    regarding purchasing all the parts are available separately so if you don't need a BDR91 to control boiler you can buy the (spare) controller, R8810A1018 and either desk or wall mount

    parts list on back of brochure
    http://www.honeywelluk.com/Documents...20approved.pdf
    It is actually cheaper to buy the evohome Connected Thermostat Pack (ATP921R3100) and the R8810A1018 than the sum of the individual components. You will have a spare BDR91, but just eBay it.

  7. #17
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    Quote Originally Posted by top brake View Post
    using the R8810A1018 will allow the boiler to modulate rather than being switch 0 or 100% using TPI on a cycle/minimum run time basis

    the benefits of modulating the boiler include lower gas use, more efficient operation and closer more stable control

    R8810A1018 is powered from the OpenTherm terminals on the boiler so no mains supply needed

    regarding purchasing all the parts are available separately so if you don't need a BDR91 to control boiler you can buy the (spare) controller, R8810A1018 and either desk or wall mount

    parts list on back of brochure
    http://www.honeywelluk.com/Documents...20approved.pdf
    Thank you for your reply.

    Can you please direct me to instructions on how to connect the R8810A1018 to the Evohome system and to the combination boiler?

  8. #18
    Automated Home Legend top brake's Avatar
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    Quote Originally Posted by jonboy View Post
    Thank you for your reply.

    Can you please direct me to instructions on how to connect the R8810A1018 to the Evohome system and to the combination boiler?
    all covered in the evohome installation guide

    http://www.honeywelluk.com/Documents...stallation.pdf

    the OpenTherm Bridge is a 2 wire connection direct to the boiler, no power supply

    The binding is done at the boiler relay level either in guided config or under system devices

    hope this helps
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  9. #19
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    Thanks top brake.

    Is the OpenTherm setup for an appropriate combination boiler with c.h. control only, and no motorised valves, really as simple as a 2 wire connection from the R8810A1018 to the boiler and a powered ATP921R3100 linked by wifi to the R8810A1018?

    Is the existing digital timer/controller simply removed and the unused wiring sealed off in block terminals, and the Danfoss hall thermostat removed and only the power cable used to power the ATP921R3100? I suggest this latter approach just in case the Honeywell Evohome system is ever removed and the original control system reinstated reinstated.

    If so is there any other fine tuning of the combi boiler or whatever?

  10. #20
    Automated Home Legend top brake's Avatar
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    Indeed it is that simple. Note that the wireless link between the evohome controller and the OpenTherm Bridge is actually 868 MHz.

    Depends on the appliance. What do you have?


    Quote Originally Posted by jonboy View Post
    Thanks top brake.

    Is the OpenTherm setup for an appropriate combination boiler with c.h. control only, and no motorised valves, really as simple as a 2 wire connection from the R8810A1018 to the boiler and a powered ATP921R3100 linked by wifi to the R8810A1018?

    Is the existing digital timer/controller simply removed and the unused wiring sealed off in block terminals, and the Danfoss hall thermostat removed and only the power cable used to power the ATP921R3100? I suggest this latter approach just in case the Honeywell Evohome system is ever removed and the original control system reinstated reinstated.

    If so is there any other fine tuning of the combi boiler or whatever?
    I work for Resideo, posts are personal and my own views.

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