Nest Thermostat 3rd Gen and Vaillant Ecotec Plus 831

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Your boiler is wired up using Vaillant's proprietary controls. They operate over ebus and the vaillant thermostat directly controls the boiler. This is why terminals 3 and 4 on the boiler are joined together. In a traditional system, your thermostat would control the boiler SL to operate it.

Does your CH have a motorised valve? If so, you probably have a Vaillant control panel (VR65) to operate it. If you remove this, you will need to ensure the Nest is wired through the motorised valve to operate it, and the valve would activate the SL on the boiler. (Edit - saw it's a combi, and therefore will probably not have an external valve - the boiler has an internal diverter valve).

Nest gen 3 supports opentherm and this would work best with your boiler. You need an additional vaillant opentherm module to use this, though. IMO, the nest working with on/off control is perhaps a retrograde step compared to the Vaillant thermostat you have currently.

Just to add - Dan is very knowledgeable in this area and genuinely helpful with his contributions. Fact is, you have showed a complete lack of understanding of even the basics of this installation, and so for your own benefit, I think his advice is spot on. You're best off getting a professional in if you really insist on having the Nest fitted.
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According to you, I may show complete lack of understanding of basics of this installation but one thing you can't take away from me or deny is I have the tenacity to learn and I went as far as showing this by stating what goes where

I'm not sure you've read Dan's post properly. It's actually very descriptive given it's an illustration! The wires going to your Vaillant thermostat are low voltage ebus connections, not L(ive) and N(eutral). They can be disconnected from your boiler's ebus terminals and used in T1 and T2 to power your nest thermostat.

The heatlink will be positioned near to the boiler with terminals 2 and 3 being connected to the boiler's terminals 3 and 4.

The heatlink L and N should be connected to a fused spur, not directly to the boiler.

Thanks anyway!

You're welcome.
I can only apologise to all if I've misinterpreted the images posted and caused even more confusion.
Can someone clarify which Vaillant control unit that is in the picture and is it powered via ebus or does it require mains power with wifi comms?
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The wires going to your Vaillant thermostat are low voltage ebus connections, not L(ive) and N(eutral).

They are actually Brown and Blue like in the picture and not the black and grey on the boiler attached to the ebus... please see pictures.


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They are actually Brown and Blue like in the picture and not the black and grey on the boiler attached to the ebus... please see pictures.

First thing you should do is put a multimeter to them and see what voltage is across them.

More than likely they are going into a wiring box somewhere, which is why the colours do not match.
Please l ask for your assistance.

Please kindly tell me what to do in simple outlined steps without me having to read the diagram. You have seen all I have in my configuration, please let me know if you require further details.
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Isn't there some new fangled thing called "instructions" that come with the birds Nest thing, I think you get some with the boiler as if I remember correctly...
You're a real Gobshite as someone else already called you in another thread... Most of your postings are rude and never well intended! You wish you were given all the jobs instead of members asking for assistance.

Well lets see shall we:

Small pump pliers.

Or get a set of universal caps and hope it fits.


What do you mean by column rads?

Pretty much, but I'd get him to up as much as he can to 15mm.

Whatever you think it is, triple it.

The Honeywell will be better as you can adjust the tpi to work well with an oil boiler.


Time proportional integral.

The clever bit.

Insufficient bypass.

Depends on what level of control you want.

A cheaper way to get full zone control over 3 areas would be Evohome.

In the olden days, you had to manually top up your f&e.

From teh last few forum pages.

You'll find my "beligerent posts" are to those that are too lazy/stupid/arrogant to use the search button. or interpret the results. Or where they are blatantly breaking the law or putting themselves and their loved ones in danger. You are a perfect example of the all of the above.

I enjoy helping those that help themselves where they can first.

BTW I voted to remain. Am pro-immigration (quite handy considering I am married to a foreigner), and am too sodding busy for my own good at the moment. Thankfully, I can multitask though.

But you crack on and demonstrate your ignorance further if you wish.
In fact, reading back through the thread - it is you who have been the more rude and abusive IMO. yet I still posted help and advice for you. Even if you didn't understand it - which is not really my problem is it? *sigh*.

Oh well. I have a nice and warm, internet enabled, multizoned heating system ticking along nicely.... i can even see what percentage loading each room is placing on the system. (y)

Happy Days.
deletions by Mod

I'm done writing to you!
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As if anyone can read a manual. :ROFLMAO: Let alone understand one.

dam doesn't say much about you as you need to learn how to read first ;):ROFLMAO: . never mind you remind me of someone with little man syndrome :ROFLMAO:

DNA reveals that you're both cousins of Trump. Sociopaths, Psychopaths and Narcissists!
jeez you have some problems ;)

don't worry poor little man :ROFLMAO::ROFLMAO::ROFLMAO::ROFLMAO:


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