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Thread: Rooms are struggling : Higher Flow Temperature or Higher Boiler Output

  1. #1
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    Default Rooms are struggling : Higher Flow Temperature or Higher Boiler Output

    With the recent cold snap, some of my rooms have been struggling to get to their set points. I have my Flow set to 65C and the boiler can go up to 75C. But I also have my 38Kw wound down to 18Kw. Which do I increase first and why?

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    Automated Home Legend top brake's Avatar
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    Temperatures are fine, you need to remove the range rating. What boiler is it?
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    Vaillant ecoTec 438

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    Automated Home Legend top brake's Avatar
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    Easy then. The boiler auto range rating is the setting that you need

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    Quote Originally Posted by bruce_miranda View Post
    With the recent cold snap, some of my rooms have been struggling to get to their set points. I have my Flow set to 65C and the boiler can go up to 75C. But I also have my 38Kw wound down to 18Kw. Which do I increase first and why?
    The answer to that question is easy - is the boiler able to reach the set flow temperature in a timely fashion and maintain it there ?

    With a complete cold start with all radiators coming on it might take 20 minutes or so before the set flow temperature is attained and that would be pretty normal. Once the radiators are up to temperature is the indicated flow temperature being maintained ?

    If so, increasing the max power output of the boiler won't do anything. All that will do is speed up the initial cold start performance somewhat but won't help with any rooms that are struggling to reach their set points when most of the rest of the house is up to temperature - provided the flow temperature is being reached.

    So if the boiler is unable to reach the flow temperature then yes turn up the boilers maximum heat output, otherwise turn up the flow temperature a bit. Even 5 degrees will make a noticeable difference.

    For what it's worth in these conditions I've had my flow temperature at 75, and I have a mix of old and modern radiators.

    Another thing to check would be the reported heat demands from the zones in question - are they near 100% ? Also if the radiator doesn't seem as hot as other radiators despite the room set point not being reached try lifting the HR92 off and turning the black wheel anti-clockwise to see how much further it turns - you'll probably find it turns at least half a turn even if it already reports 100%. Leave it like this for a few minutes and see if the radiator gets hotter.

    If it does, you need Stroke set to 1 on this radiator. I have a couple of radiators including the living room one where the pin has to be fully out to get full flow - in stroke 0 mode it never quite moves the pin far enough to get full flow, thus the radiator heat output is limited. I don't notice this as an issue in mild weather but in the middle of winter where the room needs everything it can get I find the room wont reach the set point unless the HR92 is in Stroke 1 mode - so that might be worth a try in the problematic rooms as well.

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    Quote Originally Posted by top brake View Post
    Easy then. The boiler auto range rating is the setting that you need
    This boiler doesn't have an Auto. You must set a Max. It modulates down from whatever max is set.

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    Quote Originally Posted by bruce_miranda View Post
    This boiler doesn't have an Auto. You must set a Max. It modulates down from whatever max is set.
    Ok then you’ll have to do a whole house heatloss and adjust to suit
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    Do I set the KW to the max the system can cope with or the minimum I can get away with. I thought condensing boilers were most efficient when driven to their max.

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    Why would you think that ?

    Also as far as I can see you haven't established yet whether you need the maximum power output turning up or just need a higher flow temperature. At least you haven't told us if you have.

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    Quote Originally Posted by bruce_miranda View Post
    Do I set the KW to the max the system can cope with or the minimum I can get away with. I thought condensing boilers were most efficient when driven to their max.
    As previous recommended the best way is to do a whole house heatloss calculation. Otherwise just set it to a bit higher and see how it goes. But it is no longer -3deg...
    I work for Resideo, posts are personal and my own views.

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