Worcester 24, 28CDI Nest Thermostat

[Badger1966]

Hi all,

My first post so please be gentle. I have a Worcester 24 or 28CDI. Trying to connect a Nest Gen 3 Pro Thermostat. ST8 is mains so as I beleiev the Nest is 24v I would
attach to St13, No11 in the pic. But my boiler only has PCB solder point and no connecter as per the picture. Wondering if I can solder direct or not? And I think it would be the first two solder points, but which is negative and live? Can't find anything on the web so hoping someone can help here.

Thanks in Advance.

 

[RandomGrinch]

But my boiler only has PCB solder point and no connecter as per the picture. Wondering if I can solder direct or not? And I think it would be the first two solder points, but which is negative and live

Sorry to be blunt, but there are a few comments here that suggest you may be in over your head!
Soldering onto the main PCB would not be a good idea.

Trying to connect a Nest Gen 3 Pro Thermostat. ST8 is mains so as I beleiev the Nest is 24v

The Nest is quite happy to switch mains voltage (as long as you use the correct terminals!), so you would use the mains switching terminals (ST8) on your boiler.

Can you post a picture of the connections you have and a model year for your boiler?
Is there not an existing thermostat?

 

[CBW]

I’m struggling to see where it’s a soldered point on the pcb.

 

[RandomGrinch]

I’m struggling to see where it’s a soldered point on the pcb.

I'm not absolutely sure if this is the correct PCB, but if the 24V connection was supposed to be used on ST13...

then, there would be a dedicated board edge connector in place, something like...

 

[Badger1966]

Sorry to be blunt, but there are a few comments here that suggest you may be in over your head!
Soldering onto the main PCB would not be a good idea.


The Nest is quite happy to switch mains voltage (as long as you use the correct terminals!), so you would use the mains switching terminals (ST8) on your boiler.

Can you post a picture of the connections you have and a model year for your boiler?
Is there not an existing thermostat?

Hi and thanks, connecting to ST8 blows the fuse on the circuit board. And yes, I used the correct terminals

 

[Badger1966]

I’m struggling to see where it’s a soldered point on the pcb.

In the picture I posted, it shows a terminal block, ST13. On my PCB it is not there, only the solder points for the block.

 

[RandomGrinch]

Hi and thanks, connecting to ST8 blows the fuse on the circuit board. And yes, I used the correct terminals

What connections did you make between the Nest and ST8?
And the Fuse that blew was where? On the boiler PCB?

 

[Badger1966]

Sorry to be blunt, but there are a few comments here that suggest you may be in over your head!
Soldering onto the main PCB would not be a good idea.


The Nest is quite happy to switch mains voltage (as long as you use the correct terminals!), so you would use the mains switching terminals (ST8) on your boiler.

Can you post a picture of the connections you have and a model year for your boiler?
Is there not an existing thermostat?

It's old. 24 or 28CDI Worcester. connections in the pic I first posted, On the nest, terminal 2 and 3 to ST8 terminal 1 and 2 with the link removed

 

[Badger1966]

What connections did you make between the Nest and ST8?
And the Fuse that blew was where? On the boiler PCB?

On the nest, terminal 2 and 3 to ST8 terminal 1 and 2 with the link removed. And the fuse that blew was on the pcb next to the mains wire in. 5x20 2A

 

[RandomGrinch]

You don't have an ST13 connection.
There are components missing on the PCB, that would relate to the 24V controls.
Even if you could solder wires on, the circuitry to respond to the call-to-heat is missing!
ST8 is the connector to use.

 

[RandomGrinch]

On the nest, terminal 2 and 3 to ST8 terminal 1 and 2 with the link removed

Ls and Lr (terminals 2 and 3) on boiler, to Nest terminals 2 and 3...

 

[Badger1966]

Ls and Lr (terminals 2 and 3) on boiler, to Nest terminals 2 and 3...

View attachment 325465

Awesome, will give it a go. Thank you very much

 

[Badger1966]

Ls and Lr (terminals 2 and 3) on boiler, to Nest terminals 2 and 3...

View attachment 325465

Well that has worked to a certain extent, fuse isn't blowing. But, heating is not coming on. Should I be setting the installed room stat on the boiler to something specific? Or disconect it? It's in the "on" mode at the moment

 

[CBW]

Well that has worked to a certain extent, fuse isn't blowing. But, heating is not coming on. Should I be setting the installed room stat on the boiler to something specific? Or disconect it? It's in the "on" mode at the moment

Any existing room thermostat should be set to maximum and the Nest will take over. If you wanted to disconnect that we can guide you through that too

 

[RandomGrinch]

Should I be setting the installed room stat on the boiler to something specific? Or disconect it? It's in the "on" mode at the moment

Can you press the 'On' button on the "Room Stat' panel, and see if that provides an override? - I'm guessing the LED above the button should illuminate.