Nest Heatlink 3rd Generation installation issue

OK people 1st time post after trying to search and resolve my issue. Hopefully someone can point me in the right direction.

My set up is an S-plan system with a Potterton Suprima boiler located downstairs with CH and HW time control integrated within the boiler housing. Honeywell L641A1039l cylinder stat and a pair of Myson control valves located within the airing cupboard. The CH room stat is located downstairs in the hallway, sorry but I don't recall the make and model but picture to follow. The wiring centre is via a Honeywell Sundial junction box located in the airing cupboard. With this set up there are no problems with the system and all is working as it should be.

After installing the Nest Heatlink and Thermostat I'm having issues with controlling the heating system correctly. With the hot water disconnected within the Nest thermostat setup I can control the heating system without issue. With the hot water set to on/off within the Nest thermostat the heating system runs continuously e.g. thermostat set to 18 and showing room temp as 25 but system running with CH 2 way valve open and boiler running along with pump. Before I get to engrossed with the Nest system setup via the thermostat can people take a look at my wiring to see if there are any apparent errors.

Original time control within boiler housing


Honeywell cylinder stat



CH 2 way valve


HW 2 way valve



Room stat in hallway original wiring



Honeywell Sundial wiring centre (original setup)



Nest Heatlink wiring



Honeywell Sundial wiring centre new setup


OK I'm going to get this posted and then comeback with some additional information on the wiring.

Update as advised

Original time control wiring at boiler left as is at boiler end and control turned off. The time control wiring at the Sundial wiring centre has been removed from the programmer terminal and made safe within a new terminal block and kept seperate.

Original room stat wiring red goes to T1 in heatlink, yellow goes to T2 in heatlink, blue is blocked off at room stat but left where it is in the Sundial wiring centre. Earth left in metal box behind room stat and as was in Sundial wiring centre. Terminal 1 and 3 for the room stat wiring linked together (grey wire) in new setup at the Sundial wiring centre.

The Nest heatlink is wired as follows
Blue N goes to Sundial programmer terminal N
Brown L links to 2 and 5 and goes to Sundial Programmer terminal L
Black 3 goes to Sundial Programmer terminal CH on
Grey 6 goes to Sundial Programmer terminal HW on

I hope I've detailed everything but please let me know your thoughts as I'm going for a coffee now

First of all well done with the installation of the Heat link wiring and terminations. I've seen "professional" installations that aren't as good as that. I'll excuse you the 12v supply for the thermostat as I assume that's still a work in progress.

However, Heat links are difficult to wire and I wonder if some of the connections are properly made. It's easy to connect the terminals to the PVC sleeve instead of the conductor, I like to see just a tiny bit of copper showing out of the terminal, and I can't see this with all of the terminals. They could be OK, but best to check.

I have assumed the N and L mains supply is OK, and the links between L-2-5 are also in order.

Changing over to Nest shouldn't be too difficult, and the descriptions below relate to how to do it starting with the system was before you began.

The wires from the programmer here are disconnected [there shouldn't be any connections remaining at these terminals] and instead....



The brown wire in 'CH OUT' goes to Nest Heat link 3 'Heating call for heat'
The blue wire in 'DWH OUT' goes to Nest Heat link 6 'Hot water call for heat'

Alternatively, if you want to simply remove the existing wires from the programmer and run new ones from the wiring centre to Nest, then the new wires would connect to the wiring centre terminals below as follows:



Programmer ON CH = Nest 3 Heating call for heat
Programmer ON HW = Nest 6 Hot water call for heat

Looking at your photos it seems that this is what you have done using the Grey and Black wires from the wiring centre HW ON and CH ON to terminals 6 and 3 at the Heat link.

Assuming that the room thermostat wires here....



....are connected to the wiring centre here:



Then I would remove the old thermostat cable completely and at the wiring centre and inset a link between terminals 1 and 3 where the red and yellow wires have just been removed from. This appears to have been done OK with the grey loop.

And that should be it. No other wiring changes should be made, everything else should be left exactly as it was.

Thank you for the reply stem. So it looks like my wiring is correct, which is great to know. I will defiantly go and check that I'm clamping all the screws to copper as opposed to any PVC sleeving. Assuming no screws are clamping on PVC I suppose my next course of action would be to do a complete Heatlink factory reset and then start the setup again?

That would seem a logical step. When you use the button on the front of the Heat link to operate things manually does everything work as it should? If so, that generally means the wiring is OK.

stem said:

That would seem a logical step. When you use the button on the front of the Heat link to operate things manually does everything work as it should? If so, that generally means the wiring is OK.

Click to expand...

I've not used the Heat Link button to try things manually, but I'll give that ago when I factory reset the system.

Update
I’ve checked the wiring to make sure all screws are clamping on copper and not on the PVC and all is good. I’ve reset system back to factory settings and then reset everything. What I’ve noticed is that my phone does not show the hot water option in the app?

I’ve pressed the Heat Link for manual mode, turned cylinder stat up to call for heat. Both valves are open with orange lights on and Heat Link has lights on to indicate it’s working. How is the room stat calling for heat?

Link 1 in the top left corner of the wiring centre needs to be cut.

Johnmdc said:

Link 1 in the top left corner of the wiring centre needs to be cut.

Click to expand...

I did have a slight concern about that link but that wiring centre was not causing any issues prior to fitting the Nest Heat Link? I would’ve thought my original system control was classed as a programmer. Is that the case? If so then it’s strange link 1 should be cut but all was working ok without it being cut?

Johnmdc is correct. Link 1 joins the heating and hot water outputs together for when there is only a single channel timer used to control both heating and hot water. So one on = both on. Normally I would have checked that, but as you do have a programmer and you said it was working OK before I didn't go looking for existing problems with the wiring centre.

If you had the heating and hot water set to similar 'on' times before, you wouldn't have noticed that it wasn't working properly. However as the programmer heating control circuit has been taken over by the Nest which as well as time control it also includes the thermostat control it has become more obvious.

Previously the programmer heating output would have remained 'on' constantly when the programmer was set to be 'on' now it won't be constant it will be being switched 'on' and 'off' by the thermostat as well now so what was a permanent output will be going on & off as dictated by the Nest thermostat.

Cut that link! Well done @Johnmdc for spotting it.

Edit
The app should show the hot water, but that won't be a wiring issue.

As well as Link 1 other links should be cut for S Plan. I can't see the photo clearly enough to determine if they are or not.

Ok so it looks like I best go and cut link 1. Now I have visions of me playing out bomb disposal on one of those films on tv keep your ears open for the bang

Eureka

Johnmcd you were 100% right. I've cut link 1 and now all is working as should.

Stem, your thoughts on why my old setup was appearing to be working OK was because both CH and HW were always set to on at the programmer with the CH turned on or off via the room stat when not needed. With a family of 4 the hot water in the house is used so often there was never any point in setting it to turn off.

Just one last thing to finish the thread off, many thanks to Johnmcd and stem for taking the time and effort to help out a new posting member. If I can return the complement one day I certainly will.