Vaillant VR33 (with Nest) and VR66

[theozaurus]

Incidentally, are you able to schedule your hot water using the Nest when it's connected on Opentherm or does it work solely on the VR66 switching the system to hot water priority (upping the temp, and controlling the valves) when the nest says there is demand.

 

[asoffe]

Yes. I originally set up heating with OT and HW with switched live (HW cylinder stat and switch in Nest linked in series to VR66 cyl stat connection) but then changed the HW to OT when I received my VR10 NTC as well and it controls the schedule. I don't know how it would behave with OT HW control and cyl switched stat.

 

[asoffe]

With the NTC and Nest HW set to OT, the nest also controls the cylinder target temp as well as schedule.

 

[asoffe]

You also get better feedback with the HW via OT. The two images below both show the HW set to on in the schedule but one shows that there is no demand from the cylinder.

Cylinder temp demand

Cylinder no temp demand

 

[boxer01]

If you change from switch 230v to ot you need to put the link back into the 24v connection on the main board too

I have installed the vr33 on our vaillant ecotec plus. At first I could not get it to work because I hadn't linked the 24v connection but once this was rectified the boiler works. I have the flow temp set at 65 deg.c but to me the ot is not modulating the boiler very well. The boiler flow is on 65 when heating is on, or off when up to temp the idea of open therm is to ramp boiler down before it reaches set temp. So it doesn't obershoot.there is no in between I was wandering if settings on boiler need to be adjusted to accommodate the vr33 or do I need to link ebus connections on PCB as well as the 24v connections.

 

[asoffe]

Are you using a Nest with OT? If so, True Radiant needs to be enabled on the Nest for it to set the flow temp. On the Vaillant you can also see the ebus target temp (D.9 on the EcoTec Plus 624) (flow temperature requested by the Nest) in the settings to see what is being sent. Mine is definitely modulating down. If it has a large temperature difference it will fire at max set temp (75 in my case) and modulate down as it approaches the target room temp (44 at present).
The ebus connections should not be joined to my knowledge.

 

[boxer01]

Are you using a Nest with OT? If so, True Radiant needs to be enabled on the Nest for it to set the flow temp. On the Vaillant you can also see the ebus target temp (D.9 on the EcoTec Plus 624) (flow temperature requested by the Nest) in the settings to see what is being sent. Mine is definitely modulating down. If it has a large temperature difference it will fire at max set temp (75 in my case) and modulate down as it approaches the target room temp (44 at present).
The ebus connections should not be joined to my knowledge.

Hi thank you for replying yes I am using a nest 3rd gen stat but true radiant is off as the heating was coming on too early especially in the mornings, to achieve 21 at 7am the heating was coming on at 0330 or earlier. so are you saying without the true radiant heat feature the boiler will not modulate down on approaching set temp.

 

[asoffe]

Yes as per Google's article here: True Radiant - Google Nest Help - https://support.google.com/googlenest/answer/9250165#zippy=%2Clearn-about-radiators-and-radiant-heating%2Chow-true-radiant-works%2Ctrue-radiant-settings-and-opentherm-enabled-boilers
Its the same "learning" of how long things take that I'm guessing is related to how it works out which temperatures to set the flow.
In my experience it also takes a week or two to work out timings and temps.

 

[boxer01]

Interesting reading looks like I need to enable true radiant for boiler to modulate

 

[RGInstaller]

I am a heating engineer and wish to thank you both.

I have nest and a Vaillant ecomax but have a ecotec 618 lying on floor of loft, never bothered switching it over as it works and the lack of OT on Vaillant drives me nuts (was thinking of just dumping the free 618). I've now collected the necessary components and your posts here are the best help I've had on piecing the control system together.

I'll report back.

Thanks again