Help getting Modulation on a Worcester Greenstar 28i Junior working

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Rom
Rom ✭
in General Questions & Topics
Hi,

I've just installed an extension kit, bridge, and wireless thermostat but can't get any heating demand via toe digital connections.

My boiler is quite old, but has digital terminals, labelled B B. As per Tados professional installer manual, I've connected these to the extension kit. Switch in position 1. Set the TS to D17.
System is all connected, online etc. But I get no response from boiler when putting heating on.
Hot water works fine.

I have tried swapping the wires round, as boiler isn't labelled for polarity. The extension kit powers up with it either way. But still no firing of boiler.
I have tried the switch in position 2. No change.
I have tried a link wire in the boiler between L and LR. This made the fans in the boiler spin up and down continuously, I turned it off and removed it after a minute or so as it wasn't the normal start up cycle.

I've currently got it wired up just as relay control, and it's all working as expected.

But the whole point of buying the extension kit, was to get modulation via the Bosh HT Bus B B terminals.

Am I missing something?
Not had a reply from support (it is the weekend I guess) , so thought I'd try here.

Comments

  • johnnyp78
    johnnyp78 ✭✭✭
    edited October 2022
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    The switch on the extension kit makes no difference on digital connections. Do you have a timer on the boiler? If so, is it set to always on?

    Also when you say the hot water works fine, does this mean you have a separate hot water tank? You can’t normally use a digital connection with a system boiler.
  • Rom
    Rom ✭
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    It's a combi boiler. No separate tank.

    The boiler fires when the hot tap is turned on. Guess that's it 'demand' signal for HW.

    There is no timer or anything else. When wired as relay, it all works fine, it responds to demand from TS.
  • Rom
    Rom ✭
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    Update :

    It's now working via the digital B B connections.
    I had to bridge Ls to LR inside the boiler.

    Now responds to heating on / off commands from Tado app.
  • Joshimitsu
    Joshimitsu ✭
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    Hi @Rom !

    Really strange coincidence that you posted this thread so recently and your resolution this morning, as I have the exact same boiler as you and am looking into what I would need to get modulation working with my tado setup!

    Am I to understand you are using the discontinued "tado Extension Kit" (EK01-TC-UK-03) ?

    My setup currently uses the UK wireless receiver which I had no bother setting up to replace the Hive system the previous owner had. I just mapped over the different cables between the two systems. Unfortunately there were no "left over" cables, so I assume these "B B" connections are inside the boiler and the previous installation wasn't using them either.

    Do you have any links to this installer manual you referenced? I checked the PDF for the boiler I found on Google but found very little of use in there in terms of explaining how to get the modulation working. In fact, until I read this post I was starting to wonder if the boiler even supported modulation.

    Really appreciate it in advance if you take the time to respond!

    Josh

  • johnnyp78
    johnnyp78 ✭✭✭
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    @Joshimitsu your boiler supports modulation (and does modulate) but I’m afraid the uk wireless receiver doesn’t, so can only tell the boiler to turn on and off. Unless you get an extension kit, eu wireless receiver or wired thermostat you won’t have a digital connection.
  • Joshimitsu
    Joshimitsu ✭
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    @johnnyp78 yes I undertand that, but thanks for clarifying.

    The problem I am having is trying to find any documentation that shows that this boiler supports modulation and exactly what type and what connections are available. I am unable to open the cover as (I believe) it is a sealed unit.

    If I am going to order an extension kit and have an engineer round to open the boiler, I want to be sure exactly what it is that I'm going to be wiring up, and that it is going to produce the desired results. Otherwise, it would be a wasted callout.

    I have read through a number of PDFs for this boiler at this point, and whilst they do mention modulation, they are non-specific, and it is not mentioned in any of the included wiring diagrams.

  • reetep
    reetep ✭
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    Hi @Joshimitsu, did you get this working? Could you please share any links to documentation etc that would help?

    I too have this model of boiler and I am looking to get modulation working with the tado wired thermostat.

    Thanks in anticipation, Peter

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