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Thread: Help with Evohome / Opentherm / Intergas

  1. #221
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    Quote Originally Posted by The EVOHOME Shop View Post
    As top brake has said, the spec does not require the master to set Tmax. As much as we stamp our feet, Honeywell have followed the spec laid down by the OpenTherm Association. Don't you have an Intergas boiler and can set Tmax at the boiler anyway?
    Ok, so it's not mandatory, but is it optional?

    To answer your question: I do have an Intergas boiler and I set Tmax on the master controller in the hallway.

  2. #222
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    Quote Originally Posted by blowlamp View Post
    I've cut & pasted a few things below from tinternet.

    Quote:
    While shopping for Opentherm equipment with home automation in mind, it can be useful to have some idea to which extent boilers and thermostats support the opentherm protocol. Only some messages are mandatory (ID's 0, 1, 3, 14, 17, and 25), all others may or may not implemented. (Yes Daalderop, support for MsgID 14 is mandatory.)

    Which I think refers to things in this picture.

    Attachment 1059

    So is one to conclude that MsgID 14 governs the maximum flow temperature and is required in both boilers and controllers?
    ID 57 is Max CH Water Setpoint, not ID 14, which is the modulation of the boilers fan I believe... Limiting the fan modulation wouldn't stop the boiler hitting 88 degrees before you ask, it would only limit it doing it as fast...

  3. #223
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    Quote Originally Posted by The EVOHOME Shop View Post
    ID 57 is Max CH Water Setpoint, not ID 14, which is the modulation of the boilers fan I believe...
    I figured this out the other night buggered if I can remember exactly what it was.... Not fan speed though

  4. #224
    Automated Home Legend top brake's Avatar
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    Quote Originally Posted by blowlamp View Post
    My boiler & controller are from different manufacturers in the Netherlands. The boiler allows the controller to set the CH maximum temperature and the controller has the ability to do it. It seems logical to me - the boiler's the slave and the controller is its master. So it's an odd thing in my view when a CH boiler master controller can't set a maximum CH water temperature limit.
    Not every boiler allows the ch Tmax to be set. So to avoid conflict Honeywell controls don't try to.

    Remember the best selling OpenTherm thermostat in NL has a Honeywell logo on it... Honeywell are experts in OpenTherm as they invented it...
    I work for Resideo, posts are personal and my own views.

  5. #225
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    Quote Originally Posted by top brake View Post
    Not every boiler allows the ch Tmax to be set. So to avoid conflict Honeywell controls don't try to.

    Remember the best selling OpenTherm thermostat in NL has a Honeywell logo on it... Honeywell are experts in OpenTherm as they invented it...
    But boilers (slave) donít have to set the max ch flow temp according to the OpenTherm spec either!!


    When both sides (master and slave) components of the control system are designed to set no value (which is possible and allowed within the specs - Honeywell/Viessmann) so the control system as a whole is not fit for purpose as has been shown. Finger pointing occurred in both directions in this case, and both were right unbelievably. (Honeywell vs Viessmann). Thatís what led me to start assessing OpenTherm itself as a specification.

    OpenTherm specification is flawed as it stands (the version I assessed)

    What Iím saying is the OpenTherm specification must be updated to dictate that one or the other (master or slave) sets a value.

    Itís irrelevant at this point taking about Honeywell EvoHome, Nest or Intergas or Viessmann etc. Fundamentally itís a spec problem that will manifest itself again and again. Because the spec allows for it.

    P.S. I still think EvoHome with BDR91 is great.

    ;-)

    Stephen

  6. #226
    Automated Home Legend top brake's Avatar
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    Quote Originally Posted by StephenC View Post
    But boilers (slave) donít have to set the max ch flow temp according to the OpenTherm spec either!!


    When both sides (master and slave) components of the control system are designed to set no value (which is possible and allowed within the specs - Honeywell/Viessmann) so the control system as a whole is not fit for purpose as has been shown. Finger pointing occurred in both directions in this case, and both were right unbelievably. (Honeywell vs Viessmann). Thatís what led me to start assessing OpenTherm itself as a specification.

    OpenTherm specification is flawed as it stands (the version I assessed)

    What Iím saying is the OpenTherm specification must be updated to dictate that one or the other (master or slave) sets a value.

    Itís irrelevant at this point taking about Honeywell EvoHome, Nest or Intergas or Viessmann etc. Fundamentally itís a spec problem that will manifest itself again and again. Because the spec allows for it.

    P.S. I still think EvoHome with BDR91 is great.

    ;-)

    Stephen
    Boilers have their own control systems that look after ignition, combustion and usually flow. The OpenTherm spec only covers communication between the master and slave.
    Most boilers have the ability to set CH Tmax and DHW Tmax on their control panel.

    Hope this helps
    I work for Resideo, posts are personal and my own views.

  7. #227
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    Quote Originally Posted by Dan_Robinson View Post
    I figured this out the other night buggered if I can remember exactly what it was.... Not fan speed though
    I think it is fan speed in the case of boilers where the fan governs the output of the appliance - I'm sure I have seen the fan speed (ID 15 graph) shown under ID 14 (max modulation value) on the OpenTherm monitor.

  8. #228
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    Quote Originally Posted by top brake View Post
    Not every boiler allows the ch Tmax to be set. So to avoid conflict Honeywell controls don't try to.

    Remember the best selling OpenTherm thermostat in NL has a Honeywell logo on it... Honeywell are experts in OpenTherm as they invented it...
    I thought I saw a flag in the protocol which communcates whether a device is a master or a slave.

    If the boiler won't allow the CH maximum to be set by the master controller, then it follows that it must be settable at the boiler.
    It would be quite bizarre for a boiler manufacturer to simultaneously deny access to this setting at the master whilst also disabling the setting at the slave.

    Wikipedia states that Honeywell sold the OpenTherm spec for £1 in 1996. That doesn't boost my confidence if it's true.
    Last edited by blowlamp; 13th August 2017 at 12:24 PM.

  9. #229
    Automated Home Ninja Dan_Robinson's Avatar
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    It was sold to be openish source. Do you have faith in Unix? How about Python?

    The controller is supposed to be the master. The boiler is the slave. To be otherwise doesn't make much sense

  10. #230
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    Quote Originally Posted by Dan_Robinson View Post
    It was sold to be openish source. Do you have faith in Unix? How about Python?

    The controller is supposed to be the master. The boiler is the slave. To be otherwise doesn't make much sense

    The only faith I have currently is in Bitcoin.

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