Nest Thermostat not firing up CH

[_Jay_]

Hi All, new here. Just connected up a 3rd Gen Nest Themostat to my vaillant 828 Turbomax Combi.
When I turned the boiler powered back on after connecting up the heat link I Set the temp on the thermostat (via app) to 30 degrees so a call for heat would be made.
Heard a click on the heatlink and the boiler fired up and rads starting warming up.
So I flicked the temp down again below the current room temperature (again via app) and the boiler stopped heating .
This indicated everything was working as expected.

However when I tried it again, the heat link clicked but the boiler never fired.
So I disconnected power to the boiler, checked all wiring (all seemed ok). So I restored power and did the same test again
Again, the boiler fired up., and then tured of when I turned the temp to below room temp.

But on second attempt heatlink clicked again, but boiler did not fire.


My previous thermostat was a honeywell which I disconnected and working without issues.
On the Boiler I have set the clock / time to the sun symbol now that I have installed the nest.

The heatlink always 'click's so the message is being received but nothing happens tat he boiler unless its the first time after i turn on the power to the boiler.

So it seems that the boiler only seems to fire up when asked to do so the first time after power is restored to it (seems odd?). Does anyone have any ideas on what could be causing this?
Thank you

 

[Deleted member 267285]

Is there a temperature dial on the boiler? If so is it on maximum? Could be a faulty timer.

 

[ianmcd]

On the Boiler I have set the clock / time to the sun symbol now that I have installed the nest.

you will have to set that timer to constantly on and the nest will overide it

 

[Deleted member 267285]

you will have to set that timer to constantly on and the nest will overide it

Thought he had with it being set on the sun switch?

 

[_Jay_]

Hi, yes boiler set to sun symbol (constant on).

 

[_Jay_]

Is there a temperature dial on the boiler? If so is it on maximum? Could be a faulty timer.

Yep there is a temp dial for water and CH and we keep both around 2/3 of th way round. The timer was working fine with the old honeywell stat so could be faulty timer but as it was working ok previously I am not sure. Going toi check all the wires again. Starting tho think this was more hassle than its worth - the schedule setup on the app seems a bit confusing! Wanting to try and set a schedule an dsee if the heating kicks in at the desired schedule time.
The relay in the heatlink is working as I can hear the click jut not sure why the boiler isnt firing.

 

[ianmcd]

post pics of the wring at the nest and at the boiler

 

[_Jay_]

Attached. I looped heatlink L over to common.



Thanks

 

[Deleted member 267285]

No need to loop live and common. The wires at heat link are these from the 3,4,5 terminals?

 

[_Jay_]

No need to loop live and common. The wires at heat link are these from the 3,4,5 terminals?

Correct, 3 4 and 5 = live, switched live, neutral in that order. Does common not need to be fed from live at the boiler if these are not looped at the heat link ?

 

[Deleted member 267285]

Yes it needs a link, just twigged how you’ve wired it up. Check your live connections at heat link, brown appears to be out slightly.

 

[_Jay_]

Fair point let me reseat that - it was a bit tricky getting two cores in there even thought its only 0.75mm cable.

 

[_Jay_]

Ok checked it all , seemed ok but reseated the cores - I had stripped a bit too much insulation of the cable hence the cores are showing but the cables are in.
Still have the same issue - powered up boiler and neat app fired up heating. After that nothing on second attempt.

I’m going to set a schedule for tonight and see if it comes on as expected.

I’ve only used hive before at my parents place and to be honest that seems A lot more straightforward to use - you can set on and off times whereas nest behaves a bit differently as you don’t have explicit on and off schedules . starting to think this is more hassle than it’s worth !

 

[Deleted member 267285]

How is the thermostat connected? Is there an i button on the boiler?

 

[_Jay_]

Thermostat is wirelessly linked to heat link. I use a Usb cable to put it into a wall socket.
there is an I button on the boiler - currently shows s4, quick doodle search suggests it means burner on. Not sure if that’s just the last action as the boiler did fire immediately after I restored power to it.
Sounds a bit odd but could there be some kind of time delay within the boiler during which a call for heat cannot be made ? I’ve set a schedule now and have set 24 degrees for 10 pm tonight , let’s see if it fires up.