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Thread: Evohome S-Plan with 3 BDR91 relays

  1. #1
    Automated Home Jr Member
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    Default Evohome S-Plan with 3 BDR91 relays

    Rather than hijack the fine tuning controls thread I thought I'd start a new one.

    I currently have 2 radiators without HR92s fitted so just latching the CH open and reconfiguring the BDR91 to boiler relay mode would then heat those radiators when just requiring hot water. Does anyone have any experience of using 3 BDR91s with an S-Plan system, i.e. one to boiler, one to CH, one to DHW?

    In theory, that should allow use of the min run time and cycle rate settings and allow me to minimise short cycling, but will Evohome do anything different in terms of the CH / DHW and Boiler control relays, e.g. will it leave the CH valve open for a period of time after the boiler relay is off (and pump overrun is active)? I think it may do this with the hot water (overrun setting?) but what about CH?

    I am just trying to determine whether its worth investing in another relay and I've seen this question asked a few times before on the forum with no definitive answer on how Evohome handles this config.

    Thanks

  2. #2
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    Confused.

    DHW = Domestic Hot Water
    HW = Hot Water.

    So you're saying you can't run the hot water at the same time as the hot water?

  3. #3
    Automated Home Legend paulockenden's Avatar
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    Quote Originally Posted by Fursty Ferret View Post
    Confused.

    DHW = Domestic Hot Water
    HW = Hot Water.
    I suspect HW = heating.

  4. #4
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    Sorry I tried to correct my post but it deleted it instead (mobile browser), but yes I meant CH sorry

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    Automated Home Legend paulockenden's Avatar
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    If you were to run with three relays I think the boiler relay would fire the boiler before the motorised valves had opened, and so the pump wouldn't be running. Now with my boiler that would be fine, because it takes an age to fire up. But I suspect some other boilers might complain.

    P.

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    Quote Originally Posted by morfsta View Post
    Rather than hijack the fine tuning controls thread I thought I'd start a new one.

    I currently have 2 radiators without HR92s fitted so just latching the CH open and reconfiguring the BDR91 to boiler relay mode would then heat those radiators when just requiring hot water. Does anyone have any experience of using 3 BDR91s with an S-Plan system, i.e. one to boiler, one to CH, one to DHW?

    In theory, that should allow use of the min run time and cycle rate settings and allow me to minimise short cycling, but will Evohome do anything different in terms of the CH / DHW and Boiler control relays, e.g. will it leave the CH valve open for a period of time after the boiler relay is off (and pump overrun is active)? I think it may do this with the hot water (overrun setting?) but what about CH?

    I am just trying to determine whether its worth investing in another relay and I've seen this question asked a few times before on the forum with no definitive answer on how Evohome handles this config.

    Thanks
    Binding a boiler relay along with both sundial relays.
    These cannot exist in the same evohome system and
    will result in random boiler firing. Figure 4 on page 83
    of the installation guide refers. If the system has been
    configured with both hot water and heating relays and
    a boiler relay, the boiler relay can be deleted from the
    System Parameters menu.
    I work for Resideo, posts are personal and my own views.

  7. #7
    Automated Home Legend paulockenden's Avatar
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    How does that square with this wording (see page from the manual uploaded in other thread):9ggiev.jpg

    That sort-of implies that in an s-plan setup you CAN also have a boiler relay, in addition to the other two.

    P.

  8. #8
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    Quote Originally Posted by morfsta View Post
    Rather than hijack the fine tuning controls thread I thought I'd start a new one.

    I currently have 2 radiators without HR92s fitted so just latching the CH open and reconfiguring the BDR91 to boiler relay mode would then heat those radiators when just requiring hot water. Does anyone have any experience of using 3 BDR91s with an S-Plan system, i.e. one to boiler, one to CH, one to DHW?

    In theory, that should allow use of the min run time and cycle rate settings and allow me to minimise short cycling, but will Evohome do anything different in terms of the CH / DHW and Boiler control relays, e.g. will it leave the CH valve open for a period of time after the boiler relay is off (and pump overrun is active)? I think it may do this with the hot water (overrun setting?) but what about CH?

    I am just trying to determine whether its worth investing in another relay and I've seen this question asked a few times before on the forum with no definitive answer on how Evohome handles this config.

    Thanks
    I am not experienced in Evo but in an S plan dont you have 2 Zone valves one for heat and one for HW so do you not configure each BDR91 to be a zone acuator and use each one to then to operate its zone valve

    So If Hot water BDR91 is on HW Valve opens and Boiler is Fired by end position limit on Valve and if CH BDR91 is on CH Valve opens and Boiler is fired by end position limit on valve

    In an S Plan normally the Stats operate the Zone Valves

  9. #9
    Automated Home Legend paulockenden's Avatar
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    That's exactly right Mylesm. The main problem is that when evohome is configured like this (without direct boiler control) you lose the ability to fine tune the boiler firing.

  10. #10
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    Quote Originally Posted by paulockenden View Post
    That's exactly right Mylesm. The main problem is that when evohome is configured like this (without direct boiler control) you lose the ability to fine tune the boiler firing.

    Thanks for confirming that do you by any chance know if I can control 3 Zone valves with 3 BDR91 relays through EVO I know the old gateway can only be bound to 2 Wireless Stats
    Can the Evo Controller handle More than 2 wireless stats

    thanks
    mylesm

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