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POTTERTON PROMAX COMBI 28 HE PLUS A minumum flow rate

Discussion in 'Plumbing and Central Heating' started by Hendersonm66, 15 Dec 2019.

  1. Hendersonm66

    Hendersonm66

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    Anyone able to help with this one.

    I need to fit a bypass valve to a POTTERTON PROMAX COMBI 28 HE PLUS A. The instructions for most of these bypass valves (Honeywell DU144 for example) seem to come with a chart where I have to refer to the pump speed and minimum flow rate for the boiler.

    This boiler appears to have a fixed single speed pump, and nowhere in the installation or user manuals mentions minimum CH flow rates.

    Of course, Potterton won't give me the information or assistance with the bypass setting not being a CH engineer. Anyone here knows how to obtain these figures?

    Cheers

    Mike
     
  2. ianmcd

    ianmcd

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    Why do you need a by-pass ?
     
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  4. Chris_W

    Chris_W

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    Boiler has automatic bypass, so as per @ianmcd any reason you need an additional one?
     
  5. Hendersonm66

    Hendersonm66

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    The supplier of an Evohome complete system with TRV's on all radiators recommends the external bypass, as did a quote for an install of an Evohome full TRV system.

    I know that the boiler has an internal bypass, I can see it on the installation manual bypassing through the DHW Heater Exchanger.

    Although not stated in the Potterton manual, other boiler manuals state not to rely on the internal bypass if all TRV's can be closed at the same time. It's a shame the Potterton manual isn't a bit more specific about the internal bypass performance.
     
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  7. Madrab

    Madrab

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    Have come across a lot of the newer Pottertons in newer builds with external bypasses, probably because they all fit them at the top of the boiler and it's easily spotted.

    Even with the internal BP though, it may not be able to allow enough heat dissipation/flow through the HEX under certain conditions where, according to more of the MI's I am reading recently, it shouldn't be considered as a substitute for an external one, when the system design asks for one.
     
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