Page 1 of 2 12 LastLast
Results 1 to 10 of 14

Thread: Evohome + which OT Boiler?

  1. #1
    Automated Home Sr Member
    Join Date
    Mar 2017
    Posts
    92

    Default Evohome + which OT Boiler?

    I'm planning to change my boiler soon and looking for recommendations for what would work best via multizoned evohome while fully utilising open therm.

    My current set up is a heat only boiler in S plan with unvented tank in cupboard with pump and expansion vessel.

    I'd be looking for aprox 30kw and can go to either reg or system boiler. Combi isn't really an option.

    Thanks.

  2. #2

  3. #3
    Automated Home Sr Member
    Join Date
    Mar 2017
    Posts
    92

    Default

    Looks like my options are along these lines:

    Atag iS32
    Ideal Vogue G2 32
    Ideal Logic+ Heat
    Valliant Ecotec plus +VR33

    Any thoughts?

  4. #4
    Automated Home Lurker
    Join Date
    Feb 2017
    Posts
    5

    Default

    You could add the Viessmann Vitodens 100W to that list, that's what I've just installed and am currently awaiting the arrival of the OT module, but it's working ok so far in TPI mode

  5. #5
    Automated Home Legend
    Join Date
    Jul 2014
    Posts
    1,082

    Default

    After reading the other posts regarding another Viessmann model and OT, I don't know if I'd recommend Viessmann, just yet.

  6. #6
    Automated Home Sr Member
    Join Date
    Mar 2017
    Posts
    92

    Default

    It seems a lot of the combinations of boiler plus OT will work in theory, but no one seems to be posting examples of it actually working. Sadly it seems to be example after example of something not working properly?

  7. #7
    Automated Home Lurker
    Join Date
    Feb 2017
    Posts
    5

    Default

    Yes, I'm just beginning to catch up on the recent OT threads and will be interested to see if my 100W suffers the same problem of not being able to limit the CH flow temp when my OT bridge arrives. My rads are sized for a flow temp of 55 deg as it was intended to install a heat pump, so limiting the flow temp will be quite important. Very happy otherwise with the Viessmann so far though and the internal diverter valve and DHW controller work very nicely and simplify the plumbing and controls.

  8. #8
    Automated Home Sr Member
    Join Date
    Mar 2017
    Posts
    92

    Default

    Good luck - I had read about issues with the Weismann.

    Can anyone actually name any system or reg boilers that work well with multizone evohome via Opentherm?

  9. #9
    Automated Home Legend
    Join Date
    Jul 2014
    Posts
    1,082

    Default

    A Vaillant with the VR33 seems to do a good job. My real issue is around the implementation of OT itself and the fact that it runs the boilers at full for longer than it should - or at least I think so. Of course a lot better than running it at full all the time like in a normal thermostat scenario. But thank goodness the Vaillant doesn't suffer from the issue that the Viessmann has, about not being able to control what the max temperature was, that would have really got me going against OT.

  10. #10
    Automated Home Guru
    Join Date
    Feb 2017
    Posts
    102

    Default

    I'd agree - ignoring the Viessmann max CH flow temp issue - my thoughts based on observations are the same as bruce_miranda, and that "max ch flow temp" is requested for too long - right up to and a little over the set point, meaning radiator sizing for heat loss is even more crucial than before. As per this thread with the trend towards fitting larger radiators in rooms to account for lower flow temps in condensing boilers and even heat pumps, this again goes against OT requesting "max temp" which could be outside condensing ranges.

    I would think the Honeywell OT implementation as-is would be better suited to a well insulated house with very minimal changes throughout day and night, and therefore its unlikely to need to call for "max power!!". It would be in condensing mode the vast majority of the time.

    Of course, for an older solid wall, uninstalled or poorly insulated house like many in the UK, setting the night (or even day if out at work for example) temps back can produce significant savings (as I have seen). I suspect any savings I had expected for OT will not materialize due to the lack of condensing occurring during warm up from cold phases. Its is too early to say really with any accuracy however.

    A well designed system of interfaces should (in my opinion) have fail-safes/checks built in on both sides, in this case to "catch" a silly (I don't know - how about 90 degrees, nearly boiling???!) temp request and knock it down to something safe. There is no reason in my mind why in my case Viessmann are 100% accountable for the lack of CH flow temp control. This should also be configurable on the Evohome side seeing as that is the very point of OT - to be able to control the CH flow temp. Either interface can then be configured with a max value, and the lowest is then used. Simple, right?

    To have neither side check (or allow) the temp for user set config creates the situation where we have it now. A right mess and finger pointing from both sides initially. That said, Honeywell are investigating this now. Viessmann are not... I estimate I have another ~8 years or so with this boiler (~10 year life assumption), so will need to figure this out or go back to BDR91 + weather comp.

    Its a check and balance approach that seems to be needed due to clear lack of communication and understanding of how each others components in the system inter-operate.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •