Installing a NEST to a Vaillant Turbomax

[Delfi]

Hi guys,

So the mrs is relatively convinced that the thermostat doesn't work. So she's gone and ordered a Nest, which I'm going to have to figure out how to install (hopefully with a little help )

The kit
: Honeywell T40 wired thermostat
: Vaillant TurboMax Combi 824

So currently we have a Honeywell T40 wired as below:

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• Delfi
• 1 Feb 2015
• 1

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• Delfi
• 1 Feb 2015
• 1

So first up - just out of interest how can i ascertain whether the current honeywell is/was working? Not that I'm (yet) too skilled with a multimeter - but with it set to 500v AC, I seemed to register no voltage at all across any of the terminals shown in the pictures - does that mean the thing isn't wired up - or I'm using the multimeter wrong? The temperature switch does 'click' around about the right temperature - but the boiler doesn't respond - is the Thermostat a bit mechanical? Surely switching the thermostat all the way down should stop the boiler from working?

Well, one way or another that's going - its just whether I then wire the new Nest Thermostat to that or plug it in somewhere else.

Link to Nest install guide:

http://support-assets.nest.com/images/tpzimages/Nest-Thermostat-Installation-Guide-UK.pdf

So the first question is do I have a junction box? Here's a picture of the bottom of our boiler. I don't see any external boxes so I'm guessing the thermostat is somehow wired into it. (I would have thought somewhere I should see wires coming in from the T40 - but i cant see anything - perhaps they've been cut?)

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• Delfi
• 1 Feb 2015
• 1

So I guess, after switching off the power I unscrew the main control panel:

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• Delfi
• 1 Feb 2015
• 1

which flips down? In the middle of this I should see a bunch of wires as per the wiring diagram found in the installation manual:

pg 21
http://library.plumbase.co.uk/flipbooks/RE/vaitmp824e_22531_t/vaitmp824e_22531_t.html#p=22

...and this is where my understanding gets a bit thin. With the aid of camera (keep a track of what things used to look like), the installation manual of the boiler and the installation guide to the nest all in front of me I should be able to figure it out...right?

Anyone got any good pointers at this stage? or any bits of kit I need to have to enable this to go smoothly?

Thanks in advance - I may very well be asking a few more questions shortly!

 

[muggles]

If there's no voltage there when the heating is calling then it's either not connected or the connections on the board in the boiler aren't working.

As you have a combi boiler it's unlikely that there will be a wiring centre anywhere, you just need to wire the Heat Link into the boiler using the connections currently occupied by your existing programmer

 

[Delfi]

Thanks

Flipped open the main unit on the boiler today, picture below:

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• Delfi
• 2 Feb 2015
• 1

So i think Nest will wire into 3,4,5

Would I be right in deducing that the lack of any wiring there indicates that the thermostat (as previously described) definitely isn't wired in (and appears to be redundant furniture in the house)?

 

[bazdaman]

The red linkis where the stat should be wired to so the wife was right the old honeywell does not work!

 

[Weedrip]

The lack of any measurable voltage at the original stat is probably because there is no Neutral on 2 to measure the voltage via lives on the red and black.

which also probably is why your original stat was not working as expected.... perhaps!

if you are unsure of the connections probably best get sparks in... no offence but pcb's can be an expensive mistake!

good luck

 

[Delfi]

Right - well that solves that. I guess I pull the old Honeywell of the wall.

Whats the best way of dealing with the wire on that thermostat - bit of insulating tape and leave that there - or gently pull and see what happens?

Nest then will have a new spot near a plug somewhere.

Next up - wiring diagrams. And I think i need to buy some wire.

 

[Gasguru]

Your original stat should have a neutral connection to make it more accurate, otherwise fit a stat designed for 2 wires only. A common fault on the Honeywells is for the plastic to split meaning the knob rotates out of sync with the spindle.

There's plenty of postings about Nest performing worse than normal mechanical stats! Nothing wrong with a properly installed mechanical stat IMHO....trouble is most aren't and nor will Nest. So many properties aren't even balanced for a start.

 

[Delfi]

Already now staring at a Nest and wondering how it hooks up.

RIP Honeywell thermostat.

So my next wonder is how I install the heatlink - and power it. hmmm

 

[bazdaman]

Unless i have a mental block then the honeywell is NOT wired to the boiler at all!
Also with most multimeters if you was to measure between the red and black on that stat (1+3) with the stat calling then you would measure 0v even if there was 240v there!

 

[Delfi]

So I need to get power to my heat link

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• Delfi
• 2 Feb 2015
• 1

can I run a line off of that inside the boiler

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• Delfi
• 2 Feb 2015
• 1

ie connect N & L to the corresponding spots? Looks a tight squeeze to get any more cables in there. Is this the right way - do you get a splitter?

 

[Delfi]

This seems to be very informative:

https://community.nest.com/message/28982

but still does not answer my question about somehow running the power for the heatlink out from the boiler - anyone?

 

[mikeyd]

According to a post here: //www.diynot.com/forums/viewtopic.php?t=152468 , at your boiler, 3,4 and 5 are Live, switched live, and Neutral.
At the nest, 2 is Common, 3 is NO (call for heat) and obviously L and N are Live and neutral.

So, connect boiler 3 (live) to Heatlink L and 2.
connect boiler 4 to Heatlink 3.
connect boiler 5(neutral) to Heatlink N

I managed to get two cores in the live terminal of our heatlink to link across to 2, but I was using the .75mm (I think) cable which went to my old stat.

You have probably worked this out, but the actual nest controller just uses the supplied mains adapter for power, and talks wireless to the heatlink, but if you already have a cable from where you are putting the nest to the heatlink you can use the heatlink T1&T2 terminals to supply the nest controller instead of using the mains adapter.

 

[Delfi]

Before I start doing things I think it best if someone agrees with my plan:

I think there are 2 issues here (but I maybe wrong):
1) powering the Heat Link
2) controlling the Heat link

1)
Boiler L, wire to heatlink L
Boiler N, wire to Heatlink N
And this should power the unit

2)

Boiler 3, wire to Heat link 2
Boiler 4, wire to Heat link 3

But in relation to Mikeyd's post he only has wires coming out of boiler 3,4,5....(which admittedly seems neater) is it all the same at the end of the day as:

Boiler 3 = Boiler L and
Boiler 5 = Boiler N, and
Heatlink L = Heatlink 2.

I'm mostly confused at the suggestion of boiler 3 being double wired to Heatlink L and Heatlink 2.

Thanks for the pointers all - appreciate it.

 

[mikeyd]

But in relation to Mikeyd's post he only has wires coming out of boiler 3,4,5....(which admittedly seems neater) is it all the same at the end of the day as:

Boiler 3 = Boiler L and
Boiler 5 = Boiler N, and
Heatlink L = Heatlink 2.

Possibly not quite the same. I would have thought the live at boiler 3 will be 'downstream' of any fuse on the boiler PCB. If the fuse were to blow due to a fault and you were taking the live to the heatlink from the boiler supply live, then the fuse would be bypassed when the heatlink calls for heat, which could be a bad thing to happen.

I'm mostly confused at the suggestion of boiler 3 being double wired to Heatlink L and Heatlink 2

The relay contacts on the heatlink are 'volt free'. that means they could be used to switch 12Volt DC or anything else a boiler might need. In your case you need it to switch 240V so you need to link the live to the relay common which is heatlink terminal 2.

 

[Delfi]

Great news - with a MASSIVE THANK YOU to Mikeyd - I managed to successfully wire up my Nest last night, with no problems.

For ref, I ignored my earlier post and followed Mikeyd's instructions precisely.

Thanks to everyone for helping me get this completed - the mrs is now very happy.