Page 5 of 6 FirstFirst 123456 LastLast
Results 41 to 50 of 55

Thread: Vaillant flow temperature control for HW

  1. #41
    Automated Home Legend
    Join Date
    Jul 2014
    Posts
    1,568

    Default

    You can test this quite easily. I actually think one of the CYL terminal is actually supplying a 230V live and the other terminal is simply there to accept that 230V voltage via the cylinder thermostat. So no I do not think you will blow this CYL terminals with mains voltage.
    I'm going back up to my loft tomorrow to check a few things. I can check this for you. The bit I don't know is which of CYL terminal 1 or terminal 2 is 230V Live and which is expecting the 230V return loop.
    The reason this is important in your case, is because you may actually need to only connect your DHW SL output to one of the two CYL terminals.

  2. #42
    Automated Home Sr Member
    Join Date
    Dec 2017
    Posts
    71

    Default

    That's great info. Thanks very much.

  3. #43
    Automated Home Sr Member
    Join Date
    Dec 2017
    Posts
    71

    Default

    Argh, actually thought this through, and that presents a problem.

    If CYL+ always provides 230V, then I cant connect it to SL, as it will fire the boiler.

    If I do it the other way, and put the SL on CYL-, then any zone valve opening will activate DHW mode, defeating the purpose.

    That's annoying. Going to have to go down the relay route or use the DHW zone valve terminals on the VR65 to power the pump for DHW, and remove the DHW SL completely.

  4. #44
    Automated Home Sr Member
    Join Date
    Dec 2017
    Posts
    71

    Default

    Quote Originally Posted by bruce_miranda View Post
    The way I use the VR65 is by using the microswitch (grey and orange) wires in my DHW to close the CYL inputs on the VR65.
    My DHW zone valve is switched on by Evohome, but it doesn't need to be. Because 230V is going round that CYL loop, you can effectively use that as a SL for your DHW reheat cycle. You will just need to work out which of the two CYL terminals is Live 230 and which is expecting the loop back from the cylinder safety Thermostat.
    The triggering of your boiler can stay the same.
    I think I understood what you were saying now. Use the live going to the DHW zone valve to feed the CYL terminal (whichever needs voltage on it).

    That live will be coming from the megaflo overheat stat.

    Sorry, was being a bit slow there.

  5. #45
    Automated Home Legend
    Join Date
    Jul 2014
    Posts
    1,568

    Default

    Correct. I actually think that the way the CYL terminals work is similar to the 3-4 boiler SL terminals, where terminal 3 provides the 230V output and terminal 4 is waiting to receive it. In reality, no one actually loops 3 back to 4 but instead just sends 230V to terminal 4.
    You can try doing exactly that with your DHW valve. Whatever is powering that valve, send that same signal to the CYL side that needs to see the 230V.

    That's my theory ofcourse, I hope that there is no continuity test performed between those CYL terminals.

  6. #46
    Automated Home Legend
    Join Date
    Jul 2014
    Posts
    1,568

    Default

    Just checked this. Like I suspected, the Left hand CYL terminal is 230V Live. And the moment that 230V live reaches the Right hand CYL terminal, the boiler is put into DHW heating mode.
    So my solution should work for you. Just send your DHW timer Live output that is used to power your DHW valve (Brown wire) to the Right hand terminal on the CYL terminal block.
    Keep all your Orange zone valve wires as they are to fire the boiler.

  7. #47
    Automated Home Sr Member
    Join Date
    Dec 2017
    Posts
    71

    Default

    Thanks for confirming Bruce. Just waiting on my VR66 and VRC 470f to try this.

    Another couple of questions, if I may, as you understand how ebus works very well:

    1. The user on diynot has a 428 boiler and says ebus (through the VR65) is able to fire his boiler even though terminals 3/4 are not linked. I thought ebus was an "override" system, where the boiler continually fires unless ebus tells it not to? How then is he able to get SL and ebus working together?

    2. In a standard all vaillant setup with a VR65. In the absence of any override, am I right in saying the boiler will fire for DHW whenever the CYL terminal calls for it? So the VR65 sends an ebus command to the boiler. However, if you add a vaillant VRC 4xx, it is able to set a HW schedule. So now the VR65 will only fire the boiler for DHW if it is within schedule and the CYL terminals are activated. How do the ebus commands work now?

    - does the VRC tell the VR65 when to fire the boiler?
    - or does the VRC override the command from the VR65 to the boiler?

    Sorry - for the long windedness of that question. Hope it made sense. Just intrigued on how this all works, not really relevant to what I am trying to achieve.

  8. #48
    Automated Home Legend
    Join Date
    Jul 2014
    Posts
    1,568

    Default

    1. eBUS can do (atleast) two things. It can vary the required flow temperature and it can fire the boiler. In order to fire the boiler, it needs the terminals 3-4 linked. However if you do not link them and supply a switched live to Terminal 4, then eBUS simply handles the variable flow temperature required. In fact this is how I used my system for a while where eBUS was simply managing my Flow (D.9) The VR65 just adds another layer to this, i.e. it can tell the boiler if it's doing a CH or DHW reheat.
    2. In an all Vaillant solution, the CYL terminals are always linked because they go through the boiler safety thermostat. A VR10 is then inserted to tell the boiler how hot the water in the unvented cylinder is. You can vary how hot you want the water, by using the dial on the front of the boiler. The VRC then handles things like the schedule (and boiler firing). The eBUS system is an hierarchy system, so it can detect the presence of schedulers and controllers on the bus. So when a VRC is present on the eBUS, it handles the boiler firing as per it's own schedule. The VR65 doesn't fire the boiler in any case. It is always a thermostat or scheduler that does the actual eBUS boiler firing. Unless you are using a SL 230V timer. The added confusion is that the VRC, if inserted into the boiler panel acts only as a scheduler and handles weather compensation etc. But it doesn't act like a remote
    room thermostat.

    It's all a bit smart but that makes things super confusing too.

  9. #49
    Automated Home Sr Member
    Join Date
    Dec 2017
    Posts
    71

    Default

    Quote Originally Posted by bruce_miranda View Post
    In order to fire the boiler, it needs the terminals 3-4 linked. However if you do not link them and supply a switched live to Terminal 4, then eBUS simply handles the variable flow temperature required.
    This is what I'm not getting. The guy on diynot is adamant that:

    1. Terminals 3+4 are not linked. He uses SL from his motorised valves to 4 for central heating only.

    2. The DHW motorised valve orange/grey is connected directly to CYL on the VR65. Ie. SL does *not* go to the boiler.

    I double checked with him on private message, as I was sure ebus only worked if RT terminals are bridged (either 24V or 230V) on newer boilers, or 3+4 on the older 4 series boilers, like ours (which his is).

    Yet he says the boiler still fires on DHW demand. Either ebus is working without 3+4 bridged or he's got it wrong (and somehow is supplying SL to boiler).

    Not that it matters tbh. Just intriguing. I've got way too much time on my hands being off work atm. Lol.

  10. #50
    Automated Home Legend
    Join Date
    Jul 2014
    Posts
    1,568

    Default

    If the Orange wire from the DHW zone valve is indeed not connected the Terminal 4, and the guy is sure of it, then it could mean that eBUS uses a different boiler trigger when in DHW heat mode. But unless he can completely disconnect his Terminal 4, there is no way of proving that. He probably hasn't checked inside his wiring box, where it's absolutely normal to have all Orange wires connected together. Or he could also have a system where his DHW is also operating a second CH zone simultaneously, and it's that CH zone that is causing the boiler to fire. No way of knowing that. But I agree, it would be nice to know. Because that could help some people.

    Your post reminded me to make another post telling people how the VR65 does have a place even in the fancy world of Evohome/OT etc.
    https://www.automatedhome.co.uk/vbul...5511#post45511

Posting Permissions

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