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Thread: Help with Evohome / Opentherm / Intergas

  1. #51
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    Quote Originally Posted by DBMandrake View Post
    Yep,

    We've all seen that thread from October last year before in previous discussions - but it doesn't go much beyond speculation. The poster (whoever they are) is just relaying Intergas's claim that the problem is due to not modulating with multiple zones, but offers no technical details to back up this claim.

    They then go on to speculate that there is "too much data" coming from the OpenTherm bridge, but that is pure unsubstantiated speculation and to be honest, as someone who works in computers and has done a little bit of embedded development, I don't buy this argument for a second.

    In short, we really don't know what the issue is, but I cannot see how it can be related to having multiple zones. It just seems like another case of a poor OpenTherm implementation.
    I still struggle to understand when a manufacturer that developed the Opentherm protocol would not implement it correctly in its product range. I return to my earlier plea to Honeywell to spell out how they expect an Evohome/Opentherm connected boiler to respond to Opentherm control both in HW and CH modes?

  2. #52
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    This link takes you to a Belgian website. Click on CV half way down the page and it shows the boilers that they believe are Evohome/Opentherm compatible.

    https://www.thermostaatstore.be/prod...opentherm.html

    The Intergas RF range does not appear to be in the list ( country model number difference?) and some boilers with known problems are in the list. Interestingly, they call Evohome 'single zone'.

  3. #53
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    Quote Originally Posted by HenGus View Post
    Interestingly, they call Evohome 'single zone'.
    Which is effectively what it is, as far as the boiler is concerned.

    P.

  4. #54
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    I have just had a courtesy call from Atag so I raised this ongoing discussion about Evohome/Opentherm. One of their technical guys will get back to me. Of interest, I have just found this on the Vokera website:

    Quote: When the OpenTherm control is installed it overrides the controls on the boiler fascia. For example the OT Control will override the heating and hot water temperature settings on the boiler fascia. So your OT controller is now the means by which you control your heating system and boiler. It also overrides any other room thermostat or time control previously fitted to the system which may still be connected. Unquote

    The above statement does beg the question about 3rd party opentherm controls which donít have the ability to set boiler parameters, or is this set up bespoke to Vokera controls with one their own boilers?

  5. #55
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    Quote Originally Posted by HenGus View Post
    I have just had a courtesy call from Atag so I raised this ongoing discussion about Evohome/Opentherm. One of their technical guys will get back to me. Of interest, I have just found this on the Vokera website:

    Quote: When the OpenTherm control is installed it overrides the controls on the boiler fascia. For example the OT Control will override the heating and hot water temperature settings on the boiler fascia. So your OT controller is now the means by which you control your heating system and boiler. It also overrides any other room thermostat or time control previously fitted to the system which may still be connected. Unquote

    The above statement does beg the question about 3rd party opentherm controls which don’t have the ability to set boiler parameters, or is this set up bespoke to Vokera controls with one their own boilers?


    The first part of the quote is exactly how our Intergas boiler works with its Remeha iSense controller. I don't know what would happen with additional connected thermostats as we don't have any.

    I have no reason to think Vokera is unique in how it implements OpenTherm on its controls. I'd be fairly confident that the Isense would work OK if connected to a Vokera boiler and likewise with their controller connected to our Intergas boiler, althought I'm sure that certain advanced features would differ.

    As a minimum, I'd expect flow temperatures to be handled seamlessly, no matter how the components are mixed. By that I mean I'd expect to be able to set a room temperature in the knowledge the system is taking care of adjusting flow temperature - and to stay in condensing range if possible - without me having to specify it.


    Martin.
    Last edited by blowlamp; 5th July 2017 at 12:24 AM.

  6. #56
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    To digress slightly, it would seem that posters worried about Evohome over-riding their boiler flow set temperature when heating water may just be seeing normal opentherm operation. The question that I have asked Atag is whether they are happy with a controller that can demand 90C flow temperatures when their boiler specification gives a maximum of 85C flow temperature in the technical specification? That said, if my observation of my Atag is anything to go by, I suspect that the answer will be that boiler set temperature is not being over-ridden by Evohome. I have also been able to reduce the max CH flow temperature on the boiler controls. In sum, I am not sure that I am any the wiser.

  7. #57
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    Quote Originally Posted by HenGus View Post
    To digress slightly, it would seem that posters worried about Evohome over-riding their boiler flow set temperature when heating water may just be seeing normal opentherm operation. The question that I have asked Atag is whether they are happy with a controller that can demand 90C flow temperatures when their boiler specification gives a maximum of 85C flow temperature in the technical specification? That said, if my observation of my Atag is anything to go by, I suspect that the answer will be that boiler set temperature is not being over-ridden by Evohome. I have also been able to reduce the max CH flow temperature on the boiler controls. In sum, I am not sure that I am any the wiser.
    Edit:

    I have just checked boiler temperatures again after my DH ran a bath. The boiler profile is set to a max flow temperature of 70C. The output flow was showing 70C, TSet 70C and a return temperature of 65C. Clearly, the boiler is over-riding Evohome Opentherm. I suspect that if I changed the boiler profile to 80C the boiler max flow temperature would respond accordingly.

    Looking at Atag's own interpretation of an Opentherm control. It has the usual end user settings but nothing in the controller to control boiler temperatures. Indeed, the manual makes it very clear that these are set on the boiler.

  8. #58
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    What is normal under OpenTherm is that the settings that are able to be made on the master controller override the equivalents on the boiler controller. The boiler is thus controlled by those constraints programmed into the master controller, that is, the master controller becomes the boiler controller except for the more fundamental features such as overheat protection, ignition problem lockout & range rating etc.

    What isn't normal (for me) under OpenTherm is persistant demand at full CH output for 'topping-up' lost heat where a lower flame height would suffice.

    In contrast to the Atag controller you mention, the Remeha manual I linked to on the previous page of this thread (starting ~ page 20) details the included CH settings which do have priority on my system. Also note towards the end of the document the official OpenTherm logo and the V3.0 specification.

  9. #59
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    Quote Originally Posted by HenGus View Post
    Edit:

    I have just checked boiler temperatures again after my DH ran a bath. The boiler profile is set to a max flow temperature of 70C. The output flow was showing 70C, TSet 70C and a return temperature of 65C. Clearly, the boiler is over-riding Evohome Opentherm. I suspect that if I changed the boiler profile to 80C the boiler max flow temperature would respond accordingly.

    Looking at Atag's own interpretation of an Opentherm control. It has the usual end user settings but nothing in the controller to control boiler temperatures. Indeed, the manual makes it very clear that these are set on the boiler.
    The Valliants also work this way. But bear in mind the Valliants also have a VR33 stuck in the middle between boiler and OT bridge, which could easily be affecting the way the two interaction. In fact if you query the eBUS of the Valliant boiler it has both values i.e. Temp being demanded by the OT bridge as well as Max Temp it is trying to get to as restricted by the boiler controls. The Flow temp will only ever get to the lower of those two values i.e. Demanded or Boiler set.

  10. #60
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    Quote Originally Posted by bruce_miranda View Post
    The Valliants also work this way. But bear in mind the Valliants also have a VR33 stuck in the middle between boiler and OT bridge, which could easily be affecting the way the two interaction. In fact if you query the eBUS of the Valliant boiler it has both values i.e. Temp being demanded by the OT bridge as well as Max Temp it is trying to get to as restricted by the boiler controls. The Flow temp will only ever get to the lower of those two values i.e. Demanded or Boiler set.
    I'm increasingly unconvinced by this. See this graph:

    boiler-overshoot.jpg

    I'm colour-blind, so I struggle to describe this graph. The line that goes highest of all is the eBus requested temp. The spike is at 90C. The line "inside" that, is the boiler's actual target temp, and is the same as the eBus temp, except it's capped at the temp configured on the boiler - in my case 75. This /appears to be/ the temperature the boiler aims for, but it doesn't always manage. If you look at the two lines that slowly slope down during the first half of the period, the higher one is the flow temp, the lower one is the return temp. But look at 14:50... The flow peaks just over 80C (despite the boiler being configured for 75C, and having a "physical max" of 80C).

    Compare and contrast this graph:

    boiler-power.jpg

    This shows a period of heating the DHW. In this case, the eBus request is for 90, the boiler targets 75, and hits it pretty much spot on, and then gradually modulates the flame down (the bold line) as the return temps climb as the delta-T inside the cylinder narrows and there is less and less heat extracted.

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