How do you wire Nest to Vaillant Combi Boiler?

[Mr Sparkle]

Nest is not firing up boiler and I need to know whether i have done something wrong

So far here is what i've done the following wiring work

- Using 4 core cable, i've wired two cores to the L and N on both the heatlink and boiler

- The third core is connected to terminal 3 on the heatlink and the other end is connect to RT on the Vaillant boiler

- Fourth core is placed in earth terminal on both the heatlink and boiler

- Used a small piece of brown cable, connecting (jumping) both the Live in the heatlink with terminal 2 in the heatlink

Connected T1 and T2 from heatlink to V3 Thermostat

Anyone know why the central heating wont fire up?

 

[ericmark]

Nest I know, Vaillant I don't. So I am assuming Nest Gen 3 not Nest e? With Nest Gen 3 it has two methods to control boiler, one is volt free contacts, the other is OpenTherm, so to start with which method are you using?

The advantage of volt free is does not matter if boiler uses 230 volt (low voltage) or 24 volt (extra low voltage) it will still work. And since you have access to the com terminal it can work even with a C Plan.

The centre button on the heat link will work even if the thermostat is not connected, so start by pressing centre button, that is what my maintenance guy does to run it when servicing it.

This may help others, full guide here. but I have no idea what RT is? I have found one manual which says

Do not connect any mains voltage to the eBUS (+/-) and RT 24 V terminals.

so it seems likely

- Used a small piece of brown cable, connecting (jumping) both the Live in the heatlink with terminal 2 in the heatlink

Was the wrong thing to do, and you need 5 core cable or more likely two cables. Should not run low and extra low voltage together. But boiler type would help.

 

[RandomGrinch]

- Using 4 core cable, i've wired two cores to the L and N on both the heatlink and boiler

- The third core is connected to terminal 3 on the heatlink and the other end is connect to RT on the Vaillant boiler

- Fourth core is placed in earth terminal on both the heatlink and boiler

- Used a small piece of brown cable, connecting (jumping) both the Live in the heatlink with terminal 2 in the heatlink

What is your boiler model?
Assuming yours follows the standard Vaillant wiring methodology, the 230V RT terminal is the correct one to use.

Have you turned the boiler heating controls to continuously on, or is there an existing wireless receiver built into the front of the boiler?
Can you share a couple of pics?

Nest I know, Vaillant I don't. So I am assuming Nest Gen 3 not Nest e? With Nest Gen 3 it has two methods to control boiler, one is volt free contacts, the other is OpenTherm, so to start with which method are you using?

Obviously a gen 3, by terminals the OP has listed.

The centre button on the heat link will work even if the thermostat is not connected, so start by pressing centre button, that is what my maintenance guy does to run it when servicing it.

A good call, but Nest heatlinks have a reputation for failing relays, pressing the button may not give a definitive answer.

Was the wrong thing to do, and you need 5 core cable or more likely two cables. Should not run low and extra low voltage together. But boiler type would help.

Vaillant also use the RT symbol on the 230V return...

 

[Mr Sparkle]

I've attached images of the wiring so far

The boiler is a Vaillant ecotec pro 28

This is a Brand new Version 3 Nest Thermostat

Does anyone know why it's not firing up the boiler?

Have you turned the boiler heating controls to continuously on, or is there an existing wireless receiver built into the front of the boiler?

Yes, I have.

 

[RandomGrinch]

Does anyone know why it's not firing up the boiler

Looks correct to me.
If you connect the grey wire in terminal 3 directly to the brown in terminal 2 (after safely isolating power, etc.), does the boiler fire?

 

[Mr Sparkle]

Looks correct to me.
If you connect the grey wire in terminal 3 directly to the brown in terminal 2 (after safely isolating power, etc.), does the boiler fire?

Jus to so that I am clear, do you want me to do the following?

- Leave the existing brown cable in terminal 2
- Remove the grey cable in terminal 3
- Add the grey cable from terminal 3 to the brown cable in terminal 2

 

[RandomGrinch]

- Leave the existing brown cable in terminal 2
- Remove the grey cable in terminal 3
- Add the grey cable from terminal 3 to the brown cable in terminal 2

Yes,
That is what the relay in the heat link does anyway - it simply connects those two terminals together, when there is a call for heat.

 

[Mr Sparkle]

Yes,
That is what the relay in the heat link does anyway - it simply connects those two terminals together, when there is a call for heat.

Thanks.

Did the above and still nothing

 

[RandomGrinch]

Thanks.

Did the above and still nothing

Ok, so the problem may not be with the Nest.
Were there any existing controls installed before you attempted to wire the Nest?
Is there a link in the 24V RT connector?

 

[Mr Sparkle]

Were there any existing controls installed before you attempted to wire the Nest?

I inherited the boiler so can not say 'yes' or 'no' with certainty

Is there a link in the 24V RT connector?

My existing set up looks just like the pic with a link in the 24V RT connector

 

[Taylortwocities]

does the boiler fire?

After you have then turned the power back on!

Next thing is to take a steb back. Put a link in the RT connector and check the boiler then fires.

 

[RandomGrinch]

My existing set up looks just like the pic with a link in the 24V RT connector

Next step is to remove the 24V RT connector!

 

[Taylortwocities]

Next step is to remove the 24V RT connector!

I havent seen a 24v RT connector in the OP's photos.

 

[Taylortwocities]

This vid shows how its supposed to be done.
I got motion sickness watching this...

 

[Mr Sparkle]

Next step is to remove the 24V RT connector!

I removed the wire (link) between the 24V RT connector and still nothing

This vid shows how its supposed to be done.
I got motion sickness watching this...

Thanks Doc.

I have wired it exactly like the video and still nothing