Help Installing Nest Gen 3 with Vailant eco tech plus 637

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Hi Guys,

I am a little cheesed off as I have already done in 1 boiler PCB board which I will have to order in.

My Set up for the ground floor is:

1x Vailant 637 boiler which does my ground floor heating and hot water
1x Honey well programmer
1x Honey well Room stat.
and my system is Zoned.

Tried changing the programmer with the nest installed leaving the Honeywell Room Stat on the wall, just did this to test so the trigger would start my boiler going, well that was the plan. Did not plug the nest room stat in as I wanted to see if the boiler fired up.


So going by my photos on the Honeywell programmer I have from left to right
Earth, Neutral, Live, then 3 (Hot water ON) Black, then 4 (Central heating ON) Grey.

So I link the nest gen 3 as follows left t right

Neutral, Live, Loop from live to 2, Grey cable (Central Heating On) 3, loop from 2 to 4, Black (Hot Water On) 5.

I did this and my boiler would not even boot up. Well it would show for a moment a tempreature reading and showed some geberish on the lcd screen but the boiler was making no attempt to start up abd the screen would go blank, so I treid the original Honeywell programmer and still no go. Had to swap the PCB on the ground floor Boiler with my second boiler (Same Boiler make and model) and left the system with the original Honeywell programmer and it fired up.

My second floor Set up.

1x Vailant 637 boiler (PBC Not work at the moment as I had to swap it with my ground floor boiler)
1x Honeywell Programmer
2x Room Stat. One located first floor and 1 located second floor.
and my system is zoned. So if my stat is turned down on the second floor but high on the first floor I will only get heating on the first floor.

I was under the impression that the black wire is just a 240v trigger for hot water and the grey is a 240v trigger for Central heating.

What am I doing wrong?

Have I just been unlucky and the PCB should have been just fine and fired up or am I a idiot doing something terribly wrong and the boiler pcb would have went?


Please, please, please HELP!!!!!!!!!!!!!!!!!!!!!!!!!!!!
 

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  • Ground floor room stat.jpg
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  • Rear of Ground floor Programmer.jpg
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  • Nest wiring diagram.jpg
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  • Second floor room stat.jpg
    Second floor room stat.jpg
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  • Second floor prorammer and Room Stat.jpg
    Second floor prorammer and Room Stat.jpg
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You shouldn't really be taking the front case off your boiler as it forms the room seal and should only be removed and refitted by a Gas Safe Registered engineer...

It's not unheard of for Vaillant PCBs to fail just because the power has been turned off and on again. There are fuses on there though so it would be worth checking one hasn't blown before fitting a whole new PCB. I can't find anything wrong with your description of the way you've wired it up
 
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Tried to change the fuse but no good. May try again tonight and pray it wont fail the second board.
 
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So I link the nest gen 3 as follows left t right

Neutral, Live, Loop from live to 2, Grey cable (Central Heating On) 3, loop from 2 to 4, Black (Hot Water On) 5.

Should be:

Neutral, Live, Loop from live to 2, Grey cable (Central Heating On) 3, loop from 2 to 5, Black (Hot Water On) 6.

What is your boiler version? with two big dial knobs, or all push bottoms. I am thinking what is wrong with your first PCB.
 
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Its not that big.. So do you think the pcb can be sorted or does it have to be replaced?

Also cant understand why my first floor programer has a hot water wire to it. The second boiler doesnt do hot water, if I pressed the hot water button the light would come on but nothing would happen..
 
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If anyone can help with the pcb I would be greatful, i know it has 2 spare fuses which come with the boiler but theres only 1 fuse on thr pcb right, or is there a hidden one somewhere.
 
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Its not that big.. So do you think the pcb can be sorted or does it have to be replaced?

Also cant understand why my first floor programer has a hot water wire to it. The second boiler doesnt do hot water, if I pressed the hot water button the light would come on but nothing would happen..
You've got 74kW of heat...my reasonably-sized four-bed house uses 12kW. Sounds like a castle to me :p
PCBs can't be "sorted" - once they've blown, it's time to buy a new one. There are companies out there who claim to be able to refurbish them, but there's no way of knowing whether their refurbishments are safe or not so I wouldn't recommend going down that route
 
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You've got 74kW of heat...my reasonably-sized four-bed house uses 12kW. Sounds like a castle to me :p
PCBs can't be "sorted" - once they've blown, it's time to buy a new one. There are companies out there who claim to be able to refurbish them, but there's no way of knowing whether their refurbishments are safe or not so I wouldn't recommend going down that route
74kW boilers for over 500 SQM!
 
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The usual maximum heating requirement for a badly insulated house is about 100 W per square metre!

But that boiler power is only 148 W per m2 so not that much over powered.

Even so one boiler would do all the heating.
 
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Finally got it working last night. I was unlucky the first time as I did do everything perfectly however the pcb just failed. This one nearly beat me as I was very close to not trying it as I had bad fortune the first time.

You right Agile, the whole idea to have 2 boilers was if 1 went down the other could take over the whole house. I have 2 valves which I can turn to marry the 2 boilers together.

Got another question. I have wired up both Ground and First floor. The Second floor has a room stat in the hall way and doesn't have a programmer. It would work when the first floor programmer was switched on for heating. Can I split the heating call to the boiler or should I not do this. So basically loop "3" on the nest link first floor to the nest link second floor. I have 3x nest, how do I wire up the last nest?
 
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