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Thread: Evohome Opentherm - tearing my hair out!

  1. #21
    Automated Home Legend paulockenden's Avatar
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    Because of the compressed scale it's hard to tell, but it looks to me like the temperature is tracking the setpoint quite well?

    P.

  2. #22
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    Quote Originally Posted by paulockenden View Post
    Because of the compressed scale it's hard to tell, but it looks to me like the temperature is tracking the setpoint quite well?

    P.
    Yes, exactly, so why is Evohome calling for 60degrees to do this evey 5 minutes? why not a 30degree constant call to take advantage of the condensing boiler?

    If it tracks well, but only does this from MAX to off, then what's the point with opentherm? Might as well go back to the BDR91..

  3. #23
    Automated Home Legend paulockenden's Avatar
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    But do you know that Evohome is definitely calling for 60 degrees? Could it be that with your boiler modulated down to its lowest power and with slow pump speeds then it can’t go any lower than 60 degrees? Or could it be one of those boilers that, when asked for a low demand, start off at max and then slowly ramp down (I remember someone reporting this with one particular boiler on the forums here).

    Too many variables.

  4. #24
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    Also didn't you say, your boiler flow was set to 70C. It appears that for most of the time the flow is hovering around the 60C mark. So the flow is operating lower than if the boiler was run off a BDR91.

  5. #25
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    It will really help if you can track the D.9 temperatures when all of this is happening. That's the only thing the boiler cares about. It will try to match the flow to what is requested on D.9.

  6. #26
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    Quote Originally Posted by billytkid View Post
    Yes, exactly, so why is Evohome calling for 60degrees to do this evey 5 minutes? why not a 30degree constant call to take advantage of the condensing boiler?

    If it tracks well, but only does this from MAX to off, then what's the point with opentherm? Might as well go back to the BDR91..
    I think that you might be expecting too much of Evohome/Opentherm. I have never seen a flow temperature of 30C on my Atag boiler once the house is within its set temperature range. I think that Paul is correct. My boiler can drop from 24 to 5kWs. On start, the flow temperature slowly increases to the Set Max flow temperature of 70C. It will stay at 70C until all zones demanding heat are within their set range before falling back to about 47C depending on the outside temperature.

  7. #27
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    The lowest I have ever seen actually requested is 39C but more often it is about 45C. So 30C flow is not going to happen.

    chart.jpg

    See yesterday and this morning's demand. Now think if a BDR91 ramping up to the full 70C is better or OT. What luck I can clip my boiler to my chosen max of 65C. Yikes, imagine if I had a Viesmann and my radiators were running at 90C for that long!

    More notably, look how between 10pm and 5am everything is quiet at the boiler. All my set points drop to 8C overnight.

    From experience, OT works well when all zones are used. Evohome zone schedules and OT don't play particularly nicely especially if zones keep falling more than 1.5C away from their set points.
    Last edited by bruce_miranda; 30th April 2018 at 11:48 AM.

  8. #28
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    Quote Originally Posted by bruce_miranda View Post

    From experience, OT works well when all zones are used. Evohome zone schedules and OT don't play particularly nicely especially if zones keep falling more than 1.5C away from their set points.
    I agree 100%. Maximum efficiency is achieved by getting the house up to the desired set points and leaving it there. My home is also set to 8C from 10:30pm until 7.30am and the boiler has stopped firing overnight as zones now never fall that low.

    Looking at my usage monitor, the last hour has used 0.26CM3s of gas or about 3kWhs/10p.
    Last edited by HenGus; 30th April 2018 at 12:19 PM.

  9. #29
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    Quote Originally Posted by bruce_miranda View Post
    The lowest I have ever seen actually requested is 39C but more often it is about 45C. So 30C flow is not going to happen.
    I had a period of about 20 minutes on Friday 20th where mine was calling for 26C.

  10. #30
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    Hi all,

    I'm getting to the bottom of this...

    The crazy nightime high output, I think this is down to a bug in EvoHome. I use Domoticz to set actions based on my alarm system, and when going to bed it sets EvoHome into 'Custom' mode which turns off the heating downstairs, then at 1am it sets EvoHome into normal mode. It's at 1am that the crazy heat demand start. I've checked in the schedules of all devices and none of them at 1am have a setting to call for heat. Turning off the 1am reset (and indeed the going to bed custom mode) have stopped the issue.

    This is the URL I call to set the 'normal mode' http://XXXYYY:8080/json.htm?type=com...=Auto&action=1

    Can anyone replicate this?

    I've also spoken to Honeywell regarding the random calls for heat and they've said this may be down to learning - but seemingly they can't see anything extra in their systems beyond what we can...which doesnt help.

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