BDR91 to Nest (Gen 3)

[WhiteLogan]

Hello,

I've pored over the threads here and I'd like to ask if I've got my wiring right before I go ahead with switching my BDR91 heat link to the one with the Google Nest (Gen 3).

This is my BDR91:


This is the Nest wiring diagram:


Based on this should I connect it like this:

BDR91 (L) = Nest (L)
BDR91 (N) = Nest (N)
BDR91 (A) = Nest (2)
BDR91 (B) = Nest (3)

What's throwing me is the earth wire used at BDR91 (B). Is it an earth or have they used the wrong wire? It's a combi boiler too.

Thanks

 

[Deleted member 267285]

Wiring logic is fine, it’s an earth wire being used as a switch live. Bad practice, and if you’re re-using it then apply some brown sleeving or brown insulation tape. If you’ve gone through the threads, you should have seen many of us saying “wires mean nothing in a heating system”. What you need to check is if your Combi Boiler is 230vac switching.

 

[WhiteLogan]

What you need to check is if your Combi Boiler is 230vac switching.

Thanks Chris, that's very helpful and I feel reassured.

It is indeed 230V AC. However, what do you mean by "switching"

 

[ianmcd]

What you need to check is if your Combi Boiler is 230vac switching.

Doesnt Matter Chris, if he only uses the wires in A&B as the Nest is volt free switching , so will be switching the same as it always has, do not make a link between L&2

 

[Deleted member 267285]

If you look in the Honeywell it’s capable of receiving 24-230vac switching, this is the voltage used to switch the heating on and off. The newer Vaillant combi boilers use it, so although voltage to make the boiler work is 230vac, and receiver voltage is 230vac the switch heating on and off can be lower. Hope this makes sense?

 

[WhiteLogan]

do not make a link between L&2

Wilco, I've seen a few honeywell setups with this extra link, but seems redundant. Maybe they're thinking the spare L has to be connected to something.

 

[ianmcd]

Wilco, I've seen a few honeywell setups with this extra link, but seems redundant. Maybe they're thinking the spare L has to be connected to something.

It is for a different system of wiring, but yours doesnt need it and it possibly could damage some boilers if the link is used when not required

 

[Deleted member 267285]

Doesnt Matter Chris, if he only uses the wires in A&B as the Nest is volt free switching , so will be switching the same as it always has, do not make a link between L&2

Ahh, I’ve just realised, I’d just gone off the image that was posted, forgot it was volt free contacts