BDR91 to Nest (Gen 3)

Joined
4 Feb 2021
Messages
3
Reaction score
0
Country
United Kingdom
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:
20210204_143701.jpg

This is the Nest wiring diagram:
NEST 3 COMBI.jpg

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
 
Sponsored Links

CBW

Joined
26 Sep 2019
Messages
14,950
Reaction score
4,673
Location
North
Country
United Kingdom
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.
 
Joined
4 Feb 2021
Messages
3
Reaction score
0
Country
United Kingdom
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"
 
Sponsored Links

CBW

Joined
26 Sep 2019
Messages
14,950
Reaction score
4,673
Location
North
Country
United Kingdom
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?
 
Joined
4 Feb 2021
Messages
3
Reaction score
0
Country
United Kingdom
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.
 
Joined
15 Aug 2010
Messages
26,846
Reaction score
13,452
Location
Livingston
Country
United Kingdom
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
 

CBW

Joined
26 Sep 2019
Messages
14,950
Reaction score
4,673
Location
North
Country
United Kingdom
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 :oops:
 

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.


Are you a trade or supplier? You can create your listing free at DIYnot Local

 
Sponsored Links
Top