Vaillant Ecotec Plus 831 with Nest 3rd gen thermostat

[noviceDIYer24]

I had to replace my Honeywell Thermostat as the screen died and went for the Nest 3rd Gen during the Black Friday sales.

I have wired it up using the instructions I found in the post I linked below. Note, I do not have connections to T1 and T2.
But the thermostat is still not controlling the heating. I've had to put the Heatlink in manual mode for now and let the boiler schedule switch on and off heating, but really looking to be able to use the Thermostat.

Is there something I've done wrong or need to do differently?

NEST 3rd gen wiring to Vaillant combi 831

NEW WIRE - BOILER N to HEATLINK N NEW WIRE - BOILER L to HEATLINK L NEW WIRE - 24V RT to HEATLINK 2 NEW WIRE - 24V RT to HEATLINK 3 Yes Does it matter that above HEATLINK 2 & 3 it says 100-240V? And the BOILER RT says 24V... It means that the Heat link requires a mains voltage supply to power...

www.diynot.com

 

[trojanhawrs]

Post a picture of your wiring and the wiring in the boiler.

 

[Stuckinarut]

What Honeywell Thermostat did you replace? As above, wiring configuration would help. Removing the cover on that boiler needs safety checking afterwards as it forms part of the combustion circuit.

 

[noviceDIYer24]

hi, please see existing wiring attached.

 

[Stuckinarut]

hi, please see existing wiring attached.

You have room stat connections on both terminals for room stats. If you have left the old Honeywell in or it’s receiving a switch live it’ll seek both stats.

 

[noviceDIYer24]

the grey wire does not connect to anything. it's just on a block terminal.

 

[trojanhawrs]

Disconnect the black cable at both ends. Wire the black core (from the white cable) into the other RT terminal next to the grey at the boiler, and replace 2 and 3 on the nest with the grey and black (from the white cable).

 

[trojanhawrs]

And turn the power to the boiler off before you attempt this please.

 

[noviceDIYer24]

Have done that now. Still not able to get the thermostat to control the heating (i did switch the timer on the boiler to ON), i turned up the thermostat to 30c and the boiler isn't indicating heating icon. Even if i switch back to manual mode & boiler timer, doesn't seem to want to heat anymore.

any ideas?

 

[RandomGrinch]

any ideas?

Was there a link in the 24V RT connector when the Honeywell thermostat was connected and working? I.e...

Also to note, although the wiring space is tight within the Nest Heatlink, the cable grips should be used to grip the cables outer sheath, and not just the wires.

 

[noviceDIYer24]

Was there a link in the 24V RT connector when the Honeywell thermostat was connected and working? I.e...

View attachment 366138

Also to note, although the wiring space is tight within the Nest Heatlink, the cable grips should be used to grip the cables outer sheath, and not just the wires.

Done this now. It allows heating to work. I've switch the Heatlink off manual mode, doesn't feel like the boiler is reacting to me switching heat off via the app. I'll keep an eye on it for the evening.