Help wiring 3rd gen nest heat link

Back again - long story short cant get anyone to install for a few weeks so figured I continuity check the wires to see if I can sort this myself. Ive attached a full key diagram showing all the connections (to refresh the previous owner replaced the standard boiler with combi, removing water tank, etc - I have a Honeywell ST programmer and Salus stat - I would really like to be able to use the existing stat location to wire the nest thermostat to and swap the programmer to the heat link at the same location so will need to use 2 of the 3 stat wires as 12v connections to the heat link. If you need any photos or anything else to explain what I connect to what to make this work please let me know - would really appreciate some guidance on this (assuming its still possible having seen the full wiring plan!

nest install.jpg
 
If it helps to explain the current stat connections (Ive labelled all the wires like the image so its easier to sort later)

ST1 in the stat goes up to the wiring centre B which is connected to A which then goes to LR on the boiler via a choc block connection in the back of the programmer
ST2 in the stat (COM) goes to the programmer number 4 CH on
ST3 in the stat has just been cut by the previous owner and this goes to N4 (one of the 4 neutral wires) in the programmer

c through to g wires in the wiring centre have no connection going out and with the system turned on only C is a live wire.
 
ST1 and ST2 need to be joined at the old stat position to call the boiler on for heat, even with the Nest fitted - you need to join those in a choc block when the old stat is removed, otherwise the Nest receiver can't bring the boiler on. Unless you run a wire from CH on (4) straight to the boiler LR terminal. Then the previous cable is redundant and could be used for the 12v. How you get the 12v to that cable is another question, depending on whether you have a socket near the programmer spot so you can get 12v onto the other end of the cable going to the old stat position.
 
Lost me a little, could I not use ST3 in the stat which goes to a neutral on programmer as one 12v connection, and then use st2 on the stat which goes to 4 (CH on) on the programmer as the other 12v connection and then the boiler LR goes to A in the wiring centre but the wire must go through the programmer and possibly one of the 2 wires in a choc block at the back of the programmer and then remove this and wire into 4 meaning it goes straight from LR to 4. I need to translate this all to the nest heat link wiring. Not sure if this will work, ST1-B then becomes a redundant wire
 
You’ve got all the wires you need at that wiring centre.
Give your nest a live and neutral from terminals C and F.
The wire in terminal A will now be your heating on at the nest.
You will need to link the nest live to heating common.
Then use 2 wires that go to the stat from the wiring centre for your 12v supply. You’ve identified 1 so should be able to identify another.
Just wire it up temporarily for now until it’s confirmed it all works. Remove the programmer from the wall but keep all wires connected up behind it for now.
 
Once it works you can safely disconnect the programmer wired and group together the lives and neutrals and 3 and 4 individually and blank it off.
 
Mike83 said:
You’ve got all the wires you need at that wiring centre.
Give your nest a live and neutral from terminals C and F.
The wire in terminal A will now be your heating on at the nest.
You will need to link the nest live to heating common.
Then use 2 wires that go to the stat from the wiring centre for your 12v supply. You’ve identified 1 so should be able to identify another.
Just wire it up temporarily for now until it’s confirmed it all works. Remove the programmer from the wall but keep all wires connected up behind it for now.
Click to expand...

The only issue is, only 1 of the wires in the stat go to the wiring centre upstairs st1 on my plan, the other two stat wires st2 and st3 go into the programmer directly from the stat and don’t route via the wiring centre. Which is why I thought maybe if I do the following

St2 at stat currently in ch on any programmer use this as a 12v connection
St3 at stat currently in N4 in the programmer use as 2nd 12v connection
Then Intercept the the wire that goes from lr at the boiler to A at wiring centre and use this as 4 ch on on the programmer, meaning the st1 is redundant
Not sure if this will work?
 
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If you fitting the nest in the current programmer location then st2 and 3 could be used for the 12v supply.
Then the current programmer 3 would be used as nest 3.
Then link programmer/nest 3 at the wiring centre (C) with A in the wiring centre.
Think we basically mean the same thing though.
 
Ok thanks, so if I have understood correctly, I use the programmer N4 and number 4 as the 12v supplies as these go to the stat.

And assume you mean I connect D and A (not C and A) at the wiring centre which then connects the wire that goes to LR1 (A) to 3 on programmer (HW On) (D) basically using the HW on unused connection as the new CH on

Finally I need to put a small cable on the heat link from live to the 2 common, put the new CH created connection to 3 on the heat link, and then lives and neutrals in.
 
markh1 said:
Ok thanks, so if I have understood correctly, I use the programmer N4 and number 4 as the 12v supplies as these go to the stat.

And assume you mean I connect D and A (not C and A) at the wiring centre which then connects the wire that goes to LR1 (A) to 3 on programmer (HW On) (D) basically using the HW on unused connection as the new CH on

Finally I need to put a small cable on the heat link from live to the 2 common, put the new CH created connection to 3 on the heat link, and then lives and neutrals in.
Click to expand...
I wouldnt bother trying to put a link wire in the terminals are a little tight, just put the lives into a choc bloc and take two wires out of that, one to the L terminal and the other to the heating common. it is much easier and neater.
 
Yes.I meant d not c.

This is definitely more difficult to explain than just wire up.
Everything seems correct if your wiring identification is also correct.
 
Mike83 said:
Yes.I meant d not c.

This is definitely more difficult to explain than just wire up.
Everything seems correct if your wiring identification is also correct.
Click to expand...
they are very simple mate. If you look at your booklet that comes with it and look at the wiring diagram for a combi boiler you will see how simple it is, only 4 wires needed in the heat link plus your two 12v outputs to your stat
 
markh1 said:
Ok thanks, so if I have understood correctly, I use the programmer N4 and number 4 as the 12v supplies as these go to the stat.

And assume you mean I connect D and A (not C and A) at the wiring centre which then connects the wire that goes to LR1 (A) to 3 on programmer (HW On) (D) basically using the HW on unused connection as the new CH on

Finally I need to put a small cable on the heat link from live to the 2 common, put the new CH created connection to 3 on the heat link, and then lives and neutrals in.
Click to expand...

"Unless you run a wire from CH on (4) straight to the boiler LR terminal. Then the previous cable is redundant and could be used for the 12v."

As I was saying...
 
I’ve wired it up but it’s not firing up the boiler? I followed the instructions and even traced the LR of the boiler, it goes to the wiring centre and from there to number 3 of the heat link, continuity checked all fine. I put the thermostat on the wall and powered up, did all the settings so it’s clearly getting the 12v from the heat link fine.

But when I turn the thermostat dial to turn on the heating the boiler doesn’t start up, no error messages come up.
I press the heat link manual button and the lights come on to show manual heat on the heat link and the thermostat says manual heat but the boiler doesn’t fire, doesn’t make any noise, what’s very odd is I press the heatlink button to turn it off and the boiler pump starts but not lit as flame light isn’t on but I can feel water moving through the pipes and after a few mins goes off (which is like the few minutes after heating is turned off it runs the pump alone to use reserve heat). Bosch boiler has connections in the lr going to 3 on the heat link, Live and neutral nothing in ls (not changed any of the boiler wires so was nothing it ls to begin with)
 
My error clearly something wrong as the thermostat isn’t getting any power from the tf1 or 2 as just had it shut down so back to drawing board!
 
My mistake tf1 and 2 must be working, it’s just started up, I had it disconnected for a while clearly battery was too low and took a minute to get power, I checked and the thermostat states connected wires and wirelessly. Did a heat test which states radiators should be warming up but boiler hasn’t started so came up check nest online t06
 
When you set the nest up via the settings at the stat, did you choose the correct settings, radiators and no hot water?
 
Yes, it’s on Combi on/off on stat, just to update I used the test heat function on the stat and the boiler started (had to go through the boiler pre start up as power had been off) but worked fine I stopped the test waited for the boiler over run to stop and the tried the dial on the stat, turned it up and it worked so I turned it off. Then I tested the manual override button on the heat link, the lights came on but boiler did nothing, I turned it off and no noise from boiler heat link manual flame icon gone out and back to just connected light but now the stat doesnt work, turned stat up and boiler doesn’t start, it’s like the manual heat button on the heat link has stopped it working - could it be a faulty heat link?
 
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