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Thread: How to control secondary pump from Evohome

  1. #51
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    That's where the ABV should kick in to maintain the minimum flow rate. Slightly different problem to the one I described, which is inherent in any cold zone flushing water to the boiler return (this could be because DHW kicks in, instead of another radiator zone).

    A LLH would (hopefully) aid in both instances, as the hot and cold water from different zones should dilute at a slower pace in the header, allowing the boiler to sense the return temp dropping and have enough time to modulate down.

  2. #52
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    Sorry I meant that you get an S53 when the next set of cold rads call for heat, which means that now a lot of cold water is suddely rushing to the boiler. Similar to your situation.

  3. #53
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    Quote Originally Posted by bruce_miranda View Post
    Sorry I meant that you get an S53 when the next set of cold rads call for heat, which means that now a lot of cold water is suddely rushing to the boiler. Similar to your situation.
    Ah - actually good to hear I'm not the only one experiencing that issue.

    Though slightly concerned that the mix of cold water with the hot in the pipework isn't sufficient for the boiler to sense the cooling temperature fast enough. Hope the LLH achieves that.

  4. #54
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    Quote Originally Posted by bruce_miranda View Post
    Close Coupled Tees might be another option.
    That's actually what I have rather than an all-in-one LLH with deaerator and magnetic trap thingy. Same thing though, hydraulically.

  5. #55

    Default Evohome and Vaillant S53

    Quote Originally Posted by fezster View Post
    Ah - actually good to hear I'm not the only one experiencing that issue.

    Though slightly concerned that the mix of cold water with the hot in the pipework isn't sufficient for the boiler to sense the cooling temperature fast enough. Hope the LLH achieves that.
    Hi, I realise this is an old thread, but I am researching why my Vaillant (637 EcoTec Plus) is hitting so many S53 faults and then eventually F24's when it switches off.

    The Vaillant has been happy for about 10 years running with 2 external pumps for upstairs/downstairs zoning.
    I have just added an UFH heating loop (4 manifolds and about 300metres) and removed about 10 rads.
    We have also just upgraded to the EvoHome with digital TRVs and the UFH control.

    To stop hot water circulating around the entire 3 story house looking for 1 rad that might be calling for heat, we fitted 2 EH control units.
    1 controls bedrooms and has 12 zones on it.
    The other controls the UFH, 3rads and the DHW.

    Since upgrading I am getting S53 errors continuously. I have flushed the system several times to ensure there is no gunk (we have a Magna anyway).

    The flow/return differential can be as great as 30degrees. This is normally at night when most of the rads are set to 15degrees. UFH set to 21degrees.
    When something calls for heat, the return flow temperature drops dramatically and forces the S53 issue.

    We used to have 26+rads so the 37kw boiler was recommended at the time.
    We now have 15 rads, UFH and a 300litre storage tank.

    If anybody still active on this thread, were any solutions found?

    Thanks in advance

  6. #56
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    Do you have an Automatic Bypass Valve? It needs to be set correctly to maintain the minimum flow through the boiler.

    Honestly, I would advise just biting the bullet and having a Low Loss Header installed. Everything seems to work much more predictably with no need for expensive Magna pumps.

  7. #57
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    Either that, derate the boiler. I too had no end of pain with my 38KW boiler that was sized for radiators but then when we put in UFH, the heating requirements dropped. My boiler now runs at 18KW and because all my radiators aren't calling for heat at the same time, everything seems to work perfectly.
    I use a normal Alpha pump, not even a LLH.

  8. #58
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    The boiler size isn't dictated by the UFH and / or number of radiators, though. It's dictated by the heat loss of the house (in the depths of winter). The UFH/rads are then sized to meet that minimum heat loss, and preferably rads are oversized to allow lower flow temps.

    It's always a compromise because there are only a handful of days where the outside temperature is -1. I think the newer boilers are able to modulate down much further, though.

  9. #59
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    True, but besides heat loss, you also need to check what is the heat demand going to be like. When you have zoned systems like Evohome, very rarely are more than a handful of radiators demanding heat. So regardless of what you r whole house heat loss calculations say, at that moment, your heat loss is only limited to the zones being heated.

  10. #60
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    Totally agree, hence my point about a LLH making everything behave much more predictably. The LLH handles the minimum flow rates through the boiler, without having to have the compromise of an ABV which seldom works as expected.

    Range rating the boiler is really only an option if your boiler is genuinely oversized (which admittedly often happens).

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