Y plan heating with vaillant eco tech boiler and nest link

[Paulfg]

Hi there
I’m new to this site so please bare with me
After reading this post I appear to have a similar problem since I had my boiler replaced to a valiant eco tech plus and a new nest system installed
Basically the heating remains on constant until I manually select heating off and call for HW to drive the valve back to default position
I’m going to review the wiring centre and see if I can replace it with a wago L32 box
The only cable that puzzles me is a black which I suspect is coming from the boiler and connects with the live of the pump

Any suggestions as to what other core colours should come from the boiler and what their function is?

The new vaillant boiler was installed about 2020 but I thought it may be my 3 port valve so I have put off replacing it until now
But it sounds like it may be something to do with the feeds (switched or otherwise) coming from the boiler
Didn’t want to go into the boiler wiring and thought I may be able to fix it at the wiring centre?

 

[Paulfg]

Here are some photos of my wiring centre
Not a pretty sight
The only cable I’m not sure of is the cable from the boiler
I can see that the pump live (brown) is connected to a black but to be really sure I will need to strip it all out and mark up as I go
Red blue and yellow come from nest terminals 2, 4 and 6 respectively

 

[RandomGrinch]

Red blue and yellow come from nest terminals 2, 4 and 6 respectively

Do you mean 3, 4 and 6?
Can we see a pic of the Nest wiring?

 

[Paulfg]

Sorry yes 3, 4 and 6 see photo

 

[Paulfg]

Any thoughts on why the heating does not turn off when nest stat reaches desired temperature?

 

[Stuckinarut]

Faulty motorised valve or link left in boiler

 

[Paulfg]

Thanks for the response
I’ve heard about this link in the boiler but didn’t want to believe a heating engineer would leave the boiler installation like that
What link is it that needs to be removed if it is not a faulty 3 port valve?

 

[Stuckinarut]

It’s a 24v link that comes from the factory. Before we do this, you have a Vaillant. Is there a time clock fitted to the front?

 

[Paulfg]

No it’s a 2020 model with lcd screen
See photo

 

[Stuckinarut]

Did fault always occur or as it a recent thing?

 

[Paulfg]

Always been operating like this and not been able to get heating engineer to return!
After much research and investigation my next step was replace the three port valve but if it is a simple matter of an error on the boiler electrical installation then that may be easier to do?

 

[Stuckinarut]

Yep, sounds like the link has been left in then. Removal of the cover shouldn’t be done by a diyer, but if the link is in and it takes about a minute, I’d say you’re fine. You’re looking for a red link on the 24v side in the pcb, just make sure you have the power off too. Also, make sure the wiring has been done on the mains side. If not, then it’s likley something else. If you’re unsure post a photo of the wiring at the pcb.

 

[Paulfg]

Thanks very much for the advice to the attached photo of the supply cables to the boiler isolation switch and will try and get to the PCB tomorrow
I’m guessing (but will look at the manual) that the whole front panel needs to come off to access the electrics

 

[Stuckinarut]

Thanks very much for the advice to the attached photo of the supply cables to the boiler isolation switch and will try and get to the PCB tomorrow
I’m guessing (but will look at the manual) that the whole front panel needs to come off to access the electrics
View attachment 376671

That’s the boiler switch! Yikes, starting to think it could still be a wiring issue then. A boiler should be via a fused switch or removable plug.

Yes, front cover to be removed, then access the pcb via the drop down panel

 

[Paulfg]

Yep
That’s the cables from the wiring centre to a simple light switch on the wall adjacent to the boiler
Then the 5 core to the boiler