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Thread: New Boiler - No Pump Overrun

  1. #1
    Automated Home Jr Member
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    Default New Boiler - No Pump Overrun

    Hi all,

    I've had Evohome for about 3 years now, but am about to extend the system from 8 -> 10 HR92s (all rads) and change from a y-plan to an s-plan as part of a new boiler installation.

    I will configure the upgraded system as per figure 4 in the Evohome installation guide, with the heating zone valve locked open, one BDR91 acting as DHW relay and the other as a remote Boiler relay. I will clear and rebind as part of this upgrade.

    My major concern is that the new boiler my trusted installer is suggesting to install is a Baxi EcoBlue Advance Heat only, and this model is not wired with a permanent live and has no pump override feature. Are there any downsides to not having a boiler pump overrun when using Evohome?

    Are there any complete wiring diagrams for figure 4 available?

    Thanks in advance for your help,

    Dave

  2. #2
    Automated Home Ninja
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    You'd need to read the boiler installation manual to find out if they have any specific recommendations for pump overrun. However, it is generally recommended to have one to reduce thermal shock in the boiler heat exchanger. If you have one, you then need some kind of bypass so that it can still pump successfully when all the valves are closed.

  3. #3
    Automated Home Jr Member
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    Hi,

    Sorry if my original question wasn't clear.

    It is exactly the boiler manual that states there is no overrun and no need for one. My old boiler has one.

    I am wondering what effect this will have on the Evohome control, e.g. when the radiator valves throttle back, but maybe the pump on the old boiler would still have been running, extracting residual heat out of the heat exchanger. On this new boiler the flow will stop as soon as the demand stops?

    The boiler should be fine, as it is designed to operate in that way, but it is the effect on room temperature drops or overshoot that interests me.

    Thanks,

    Dave

  4. #4
    Automated Home Guru
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    Surely EvoHome will learn the behaviour of the new boiler and adjust accordingly?

  5. #5
    Automated Home Jr Member
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    Quote Originally Posted by rotor View Post
    Surely EvoHome will learn the behaviour of the new boiler and adjust accordingly?
    That's exactly what I would hope for, but its quite different to the old behaviour.

    Incidentally, I used to get some quite big overshoots of temperature, so in that regard it might be better if hot water stopped being delivered to the rads when the Boiler Demand Relay stopped...

  6. #6
    Automated Home Legend paulockenden's Avatar
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    If you've got a new boiler I'd be tempted to completely trash Evohome and set it up again from scratch so that it re-learns (and remember not to fiddle for a couple of weeks!). The dynamics of your system will have changed considerably.


    P.

  7. #7
    Automated Home Jr Member
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    Hi,

    Actually, I'm now on the verge of changing to an Intergas Compact HRE 24 OV, which my installer is also happy to fit for me.

    Then I will probably but the newer WiFi Evohome with an Opentherm Bridge later in the year.

    Thoughts?

    Dave

  8. #8
    Automated Home Guru
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    Quote Originally Posted by thepook View Post
    Hi,

    Actually, I'm now on the verge of changing to an Intergas Compact HRE 24 OV, which my installer is also happy to fit for me.

    Then I will probably but the newer WiFi Evohome with an Opentherm Bridge later in the year.

    Thoughts?

    Dave
    I have intergas rapid boiler with opentherm bridge and Evohome with HR92 actuators on all Rads except one for Bypass I use DTS92 Wall Mounted Temp Sensors for Zone Temp measurement and I find it works really well very stable Temp control no overshoots etc but the key is to leave it alone to do its job

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