Honeywell ST6400C to Nest Gen3 -

[Jaycx]

Ok so all I have done so far is followed the instructions from the first posts

Which were how to connect the corresponding Honeywell wires to the nest wires

The grey wire is coming from the boiler that was wrapped around the red/orange wire into the terminal block and the yellow wires were paired together too

At the motorised valve I have attached some pictures of the wires going in

 

[Jaycx]

Ok this is really confusing me

So when I wind the stat up and call for heat the boiler is not firing I can see there is the demand for heat at the heat link using a electrical screwdriver you can see the light glow and also hear the click any ideas?

The yellows that are into the same terminal block are joined together

There is a red into a different section of the same terminal block this is then connected to the grey cable which is coming from the boiler

The red cones from one of the cables which the yellow has come from .

 

[Jaycx]

Ok so it appears as though with the Honeywell Stat cranked up and then demanding the heat from the nest stat by turning that up the boiler kicks in

I’d ideally want the Honeywell gone off the wall so the nest can replace it so your guidance on that would be much appreciated!

 

[Jaycx]

The wires go to the terminals that have the same function.

View attachment 374370
View attachment 374371

N=N
L = L
1 HW Off =4 Hot Water Satisfied
3 HW On =6 Hot Water Call for Heat
4 CH On = 3 Heating Call for Heat

As you have figured, Nest terminals L, 2 and 5 should be connected together.

The Nest Thermostat is connected to T1 and T2

I don't see an earth connection at the existing programmer, although if it's mounted above a metal box it may be connected to that.

The existing room thermostat should either be set to its maximum setting to prevent it interfering with the Nest, or decommissioned by removing it and making a wiring modification to close the circuit that its removal will have left open.

What wiring mod needs to be done so the old stat can be deconissioned?

 

[Stuckinarut]

What wiring mod needs to be done so the old stat can be deconissioned?

How are you currently powering the Nest thermostat? @stem said use T1 and T2

 

[Jaycx]

I’m using the USB port on the back

I can’t use the T1 / t2 as the cable we thought we could use isn’t what it was

There’s two yellows into a terminal block and a red wire and a switch grey cable going the the boiler

The red becomes live when the CH is ON my guess is there is a need for alteration to the wiring in the wiring box before I can use them?

 

[RandomGrinch]

I can’t use the T1 / t2 as the cable we thought we could use isn’t what it was

But you still haven't answered?

does the red wire from terminal 4, come from the same cable as one of the yellows in the terminal block?

 

[Jaycx]

But you still haven't answered?

Sorry I missed that question

So one of yellow cables shares a red which connects to the grey cable coming from the boiler

The other yellow has a red which goes to 3 on the heatlink

 

[RandomGrinch]

Sorry I missed that question

In post #10, or #15!

So one of yellow cables shares a red which connects to the grey cable coming from the boiler

The other yellow has a red which goes to 3 on the heatlink

That is exactly how I have suggested your circuit has worked in all the previous posts.

The red Wire that now goes to terminal 3 of the heatlink, went to terminal 4 of the ST6400c - heating on....

Then behind the ST6400C, if you follow the red wire from terminal 4, it should come out of a red, yellow and blue triple and earth cable.
If you follow the yellow wire from this cable, I believe it links to another (yellow?) wire in a separate terminal block.

Take the other yellow Wire from the terminal block (the one that shares a Cable with the red Wire that connects to the grey Wire to the boiler), and put it into the heat link terminal 3, instead of the red Wire.

That should leave a Cable with a loose red and yellow wire. Check the blue wire is also loose and this Cable can be used for T1 and T2.

Edit: just to add - check the heating works correctly with the yellow wire connected to heatlink terminal 3 , before messing around with T1 and T2!

 

[Jaycx]

In post #10, or #15!


That is exactly how I have suggested your circuit has worked in all the previous posts.

The red Wire that now goes to terminal 3 of the heatlink, went to terminal 4 of the ST6400c - heating on....


Take the other yellow Wire from the terminal block (the one that shares a Cable with the red Wire that connects to the grey Wire to the boiler), and put it into the heat link terminal 3, instead of the red Wire.

That should leave a Cable with a loose red and yellow wire. Check the blue wire is also loose and this Cable can be used for T1 and T2.

Edit: just to add - check the heating works correctly with the yellow wire connected to heatlink terminal 3 , before messing around with T1 and T2!

I’ll give this a go in the morning and feedback

 

[Jaycx]

Thats all up and running now!

Thanks to all of those who assisted. I replaced a few bits along the way older terminal blocks for WAGOs and the Fused Spur Socket which was so old

The nest is on the wall working and charging via the Heatlink too which is more than ideal.