Nest 3rd Gen with Vaillant ecotec plus 612

[SF1984]

Thanks Fezster, pictures would be great if you don't mind.

I take it you have a nest wired to each zone valve? My valves are 230v so don't think the heat link would provide enough power.

 

[fezster]

The heat link can switch 230V zone valves. Take a look at the heat link instructions and specifically the wiring diagram for s plan. Terminal 5 is 230V common and terminal 6 is call for heat going to your cylinder stat, which then supplies 230V to your zone valve.

If you measure the voltage on the CYL terminals on the vr65/66, the left hand terminal supplies 230V and is supposed to go via the cylinder stat to the right hand terminal, thus bridging it. This then results in the vr65/66 instructing the boiler via ebus to go into cylinder heating mode (ie. Boost flow temp to 80). The same can be achieved by supplying 230V to the right hand terminal alone.

 

[SF1984]

That's for your help. I could look into this method. I would need to find a way to disconnect/decommission the existing controller. I assume you have your nest display mounted on a stand?

 

[fezster]

No, both my nests are wall mounted and powered directly by the heat links (using my existing thermostat wiring, obviously now only supplying 12V).

 

[wannocks]

The biggest difference between Ebus controls and Nest is that Ebus controls the flow temperature and boiler modulation (power output) Nest is a dumb on off control with a fancy interface.
Your controls may just need commissioning properly.

 

[fezster]

Not completely true as Nest supports OpenTherm, which also controls boiler flow temps in OT compatible boilers.

I liked the Nest controls and their thermostat, but wanted to keep the weather comp and PDHW. The solution I have makes the 2 compatible.

 

[wannocks]

It is in this case as Vaillant boilers do not have Opentherm. There is an ebus to opentherm adapter but it is not supported in the UK and will invalidate the boilers warranty.
@fezster how are you switching the boiler off when you're not heating the radiators? Do you have switched live into 4 for all zones? (HTG & HW)
Curious as I've never seen this done.

 

[SF1984]

No, both my nests are wall mounted and powered directly by the heat links (using my existing thermostat wiring, obviously now only supplying 12V).

On closer inspection I have a VR61/4 not a vr65. Any ideas on the wiring?

 

[fezster]

It is in this case as Vaillant boilers do not have Opentherm. There is an ebus to opentherm adapter but it is not supported in the UK and will invalidate the boilers warranty.

Yes, the VR33. Previous members on here have successfully used it on the Vaillant 4 series boiler. I considered it, however I didn't see any great advantage to the Nest (or any thermostat for that matter) controlling flow temps without weather compensation.

The Vaillant weather compensating controls also have an outdoor sensor, rather than relying on internet data.

@fezster how are you switching the boiler off when you're not heating the radiators? Do you have switched live into 4 for all zones? (HTG & HW)
Curious as I've never seen this done.

Correct. All zone valves use the orange SL to control the boiler using on/off controls via terminal 4. The VR66 and VRC470f/VR20 are used only for modulating flow temps.