Worcester combi boiler wiring - from Honeywell BDR91 to Nest Heat Link

22 Sep 2019
Reaction score
United Kingdom
Hi All.

Apologies if this is a repeated question - I have tried to find an answer on several forums including this one, but none of the threads quite match the wiring diagram I have.

This is my current set up: https://imgur.com/a/4Ao0B1P with the Honeywell BDR91 thermostat.

If I had to guess, this is the wiring diagram (found by googling, not drawn by me): https://imgur.com/RsRXZlY

Question is, how do I wire up the Nest Heat Link?

What I would do is the following:
Blue wire on the phone - Heat Link N
Brown wire - Heat Link L
Earth colour with live switch - Heat Link L (this is the bit I'm worried about)
Grey wire - Heat Link 3
Black wire - Heat Link 2

Would this work? Am I going to fry something with the two live wires going to the same slots?

Thanks in advance.
Sponsored Links
N to N
L to L
A to 2
B to 3

Then it depends if using hard wire or wifi to the thermostat, in theory if hard wiring then the heat link should be earthed that is so the 12 volt is referenced to earth it will work without it, and the T1 and T2 wires go to the thermostat.

If using a USB powered thermostat then don't need the T1, T2 or earth.

It will be hard getting two wires into the L terminals it is quite small, however oddly over sleeving a green/yellow wire which is part of a cable is not against regulations, not having an earth cable however is, so it does not strictly comply, and one does wonder why it has been done when it seems to be part of a single cable.
Thanks for getting back to me!

The thermostat will be USB powered so no earth / T1 / T2 needed.

As per the diagram, the mains should be earthed, but nothing else is.

So just to confirm, the sleeved cable is a live too? Where should it go then in the Heat Link?
Sponsored Links

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