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Thread: Which Combi boiler works best with Evohome?

  1. #21
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    He’s set the flow temperature to 65 but I doubt he’s changed many of the other defaults. He’s not experienced with Intergas. I’ve downloaded the installation guide and I’ll have a dig into the parameters. How do you tell if it’s condensing or what efficiency it’s running at?

  2. #22
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    Quote Originally Posted by filbert View Post
    He’s set the flow temperature to 65 but I doubt he’s changed many of the other defaults. He’s not experienced with Intergas. I’ve downloaded the installation guide and I’ll have a dig into the parameters. How do you tell if it’s condensing or what efficiency it’s running at?
    I tried the flow at 60c but it was taking too long for a room to warm. 65c was better but still a time lag, noticeable on colder days. I settled on 70c.

    The power rating for CH is easily changed in the parameters. Few installers change the default. For some reason they think it has to be high.

    Condensing. I am not a physicist but understand a boiler will only properly condense with a return temperature of around 50c max. Some advice is that the differential between flow and return should be around 20c. Hence 70c becomes the optimum. Many installers and service people set flow temperatures at higher than 70c. Not knowing that the efficiency will drop. Boilers have to be rated at above 90% efficiency but are only so efficient if set up correctly. One body looking at this came to the conclusion most were not properly set up. 65c will work fine, it just takes a little longer for the house to warm up.

    To check the efficiency you need some testing gear. I don’t have that but my service man does as he has to check. In my case it was the best he had seen in a long time.

    One other point. Your boiler probably has an Eco mode. This is to keep a small amount of water hot inside the boiler so that you don’t have to wait too long before hot water comes out of the tap. I suggest you turn it off. It annoyed me to hear the boiler firing up in the middle of the night just to keep some water hot. Hardly economic. Having it turned off has caused no problems.

    Have a look at this site, there is some helpful information here of you dig around it - https://www.theheatinghub.co.uk/

  3. #23
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    Quote Originally Posted by G4RHL View Post
    I tried the flow at 60c but it was taking too long for a room to warm. 65c was better but still a time lag, noticeable on colder days. I settled on 70c.

    The power rating for CH is easily changed in the parameters. Few installers change the default. For some reason they think it has to be high.
    Thanks again. That's something that I'll have to remember to revisit when the weather gets colder. My installer mentioned that the power required for heating was much lower than for the DHW. I'll ask him about the setting when he comes for his follow up visit next week. I won't play with it before then.

    Quote Originally Posted by G4RHL View Post
    Condensing. I am not a physicist but understand a boiler will only properly condense with a return temperature of around 50c max. Some advice is that the differential between flow and return should be around 20c. Hence 70c becomes the optimum.
    Again, this is something for the heating season, I suppose. I have a digital thermometer that I can clamp to the return pipe. I'll have a read around to find out more about this.

  4. #24
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    Having just had an Intergas boiler installed, with an OpenTherm bridge, I'm impressed with the amount of additional information that has appeared in the Domoticz device list (see screenshot. Most of these items are new, as far as I can tell).
    I'm not sure how many of them are reliable. The return water temp is shown as 71.7deg but the flow temp is only set to 65, so I doubt that. External temp is spurious as there isn't a way of monitoring it. Nevertheless, thereís an impressive amount of information being fed back to Evohome from the boiler. Hopefully, Evohome will be able to use it to improve overall efficiency and comfort.

    DOmoticzAfterOTBridge.jpg

  5. #25
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    Quote Originally Posted by filbert View Post
    Thanks again. That's something that I'll have to remember to revisit when the weather gets colder. My installer mentioned that the power required for heating was much lower than for the DHW. I'll ask him about the setting when he comes for his follow up visit next week. I won't play with it before then.


    Again, this is something for the heating season, I suppose. I have a digital thermometer that I can clamp to the return pipe. I'll have a read around to find out more about this.
    I just changed it as soon as the boiler had been installed. I dropped it down to around 12kW first. No change to efficiency and then dropped it the lowest I could. Which is what is recommended by the experts. No problems. Your boiler should display the temperatures being run. When heating has been needed mine often shows 33C.

  6. #26
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    Quote Originally Posted by filbert View Post
    Having just had an Intergas boiler installed, with an OpenTherm bridge, I'm impressed with the amount of additional information that has appeared in the Domoticz device list (see screenshot. Most of these items are new, as far as I can tell).
    I'm not sure how many of them are reliable. The return water temp is shown as 71.7deg but the flow temp is only set to 65, so I doubt that. External temp is spurious as there isn't a way of monitoring it. Nevertheless, thereís an impressive amount of information being fed back to Evohome from the boiler. Hopefully, Evohome will be able to use it to improve overall efficiency and comfort.

    DOmoticzAfterOTBridge.jpg
    Being the guy who coded all this into Domoticz, I have some bad news. Evohome uses none of this information! Infact in the latest firmware, it didn't even query for this information from the OTB. I had to change Domoticz so that it would query this from the OTB instead. Nevertheless, the OTB does allow for variable flow temperatures based on actual Heat Demand. So that in itself is reason worth using an OTB.
    One BIG missed trick is that the OTB knows when there is HW or CH demand, so it could have used this data to vary the max flow needed. But it doesn't do that. It just goes to 90C max and 10C min for any heat demand. And that's a shame. And you better hope your boiler can clamp that max being requested by OTB. Otherwise you will have some pretty hot radiators.

  7. #27
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    Quote Originally Posted by bruce_miranda View Post
    Being the guy who coded all this into Domoticz, I have some bad news. Evohome uses none of this information! Infact in the latest firmware, it didn't even query for this information from the OTB. I had to change Domoticz so that it would query this from the OTB instead. Nevertheless, the OTB does allow for variable flow temperatures based on actual Heat Demand. So that in itself is reason worth using an OTB.
    One BIG missed trick is that the OTB knows when there is HW or CH demand, so it could have used this data to vary the max flow needed. But it doesn't do that. It just goes to 90C max and 10C min for any heat demand. And that's a shame. And you better hope your boiler can clamp that max being requested by OTB. Otherwise you will have some pretty hot radiators.
    That's such a disappointment! I thought Evohome was seeing and using all this information. I also wonder how much of the info shown is reliable? I'm getting "Return Water Temperature" and "Outdoor Temperature" constantly showing as 71.7 deg. Other parameters such as Boiler Water Temperature look sensible. Maybe we need a separate thread discussing Evohome and the OTB....

    My boiler is currently set at 55 deg for HW and 65 deg for CH. The CH might need to be a bit higher but I'll see how it works come the autumn.

  8. #28
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    Quote Originally Posted by G4RHL View Post
    Condensing. I am not a physicist but understand a boiler will only properly condense with a return temperature of around 50c max. Some advice is that the differential between flow and return should be around 20c. Hence 70c becomes the optimum. Many installers and service people set flow temperatures at higher than 70c. Not knowing that the efficiency will drop. Boilers have to be rated at above 90% efficiency but are only so efficient if set up correctly. One body looking at this came to the conclusion most were not properly set up. 65c will work fine, it just takes a little longer for the house to warm up.
    Unfortuately, I'm not sure how to check the return temp. Domoticz, via the OTB, lists it as a parameter but it's constantly showing 71.7 deg. I do have a digital thermometer, so I'll play with that come the autumn.


    Quote Originally Posted by G4RHL View Post
    One other point. Your boiler probably has an Eco mode. This is to keep a small amount of water hot inside the boiler so that you donít have to wait too long before hot water comes out of the tap. I suggest you turn it off. It annoyed me to hear the boiler firing up in the middle of the night just to keep some water hot. Hardly economic. Having it turned off has caused no problems.
    Thanks but the manual for mine says that Eco mode will learn patterns and won't keep heat exchanger warm overnight, for example. Hopefully, it's telling the truth! Not that I'd hear the boiler - it's so quiet and it's tucked away. I don't even hear it fire up when I'm in the next room.

  9. #29
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    There is very little two way comms between the OTB and the controller. And that's a shame.
    Also I am not surprised that some values returned by the OTB are either static or plain wrong. It all depends on what the boiler feels like providing back to the OTB when a query is made.
    In my own system the External temperature reading I get back from OT is just plain wrong. The graph is the right shape, just the values are all wrong. But I blamed that on the VR33 module that is sitting between my boiler and the OTB doing the translations between Vaillant's eBUS and OT.

    If you start another thread related to OT and Evohome, please tag me along.

  10. #30
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    @filbert doesn't your boiler have some installer or diagnostic menu that allows you to see Return temperature. It's quote a key data point for the boiler. So it must be there somewhere.

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