Nest 3rd Gemeration thermostat

[E45Y123]

Morning Ladies and Gents,

I'm after a bit of guidance regarding the Nest thermostat 3rd Generation please...

My heating system is a Glow worm 18hx system boiler. I have a hot water cylinder pump, only radiators all round, mid position valve, Y plan wiring centre.

So my issue... my old programmer broke with a fizzle and pop so I thought now was a good time to bring part of my house to the future.... I have followed the wiring diagram that came with the new wiring centre and the nest, but my boiler runs constantly. I have no control over the heating ornhot water at all. I have turned the heating off, the hot water off bacteria prevention off on the thermostat. So with everything OFF the boiler fires and runs (it ran most of the night and my house was quite warm...). The thermostat itself is wored to the 12v side and linked through the old stat cable... The heat link is as the instructions terminal 2 and 5 being linked across with the live in... I'm not sure it it's right the at the heat link but I checked the voltage across terminal 3 and N, 4 and N, 6 and N and I have 240v even when the heating and hot water is off...

I have had the motorised valve replaced also as I thought that might have been the problem.

I have tried the various reset procedures that Google says to try...

I'm hoping someone can point me in the right direction... even if it's a faulty unit...

The heating system was working before
I have tried resolving the issue with Google... no help at all...

Sorry I will attatch some more pictures when I am home if required...

Many thanks in advance for any help x

 

[Gasmk1]

I found that fitting nests to y plan was one of the hardest, especially whe old systems wired by electrian with earths and neutrals sometimes used as switch lives, you will have to trace all wires as you have a permanent live wired in somewhere

 

[Gasmk1]

How to install Nest thermostat on a Y plan heating system (UK) - Urban plumbers - https://www.urbanplumbers.co.uk/how-to-install-nest-thermostat-on-a-y-plan-heating-system-uk/ if you are struggling try a nest pro near you

 

[Deleted member 120897]

A photo of wiring center and heatlink would be of use.

 

[E45Y123]

A photo of wiring center and heatlink would be of use.

Please see attached for reference... I have removed the cylinder stat cable as it's very short.

The boiler cable has 5 wires, L, N, E and 2 blacks, 1 is the switch or R and the other is pump, I have bellied these through so they are the correct way round...

So while the heat link is in normal operation, but with heating and hotwater off I have 240v at the boiler switch return/orange and when I put it into manual mode that terminal drops to 30v ish...

 

[Deleted member 120897]

Hard to tell, but you may have a permanent live feeding your boiler pump live.

 

[ShaunCorbs]

Stick the old existing black core to the pump live

Also the boiler cable (right hand one with the two wagos) has two black cores but on the plug there’s only one

 

[E45Y123]

Stick the old existing black core to the pump live

Also the boiler cable (right hand one with the two wagos) has two black cores but on the plug there’s only one

On the plug, it's a 5 core newish cable, goes into a 3 pole isolator which has a 5 core (brown, blue, earth plus 2 black coming out) so the black with 2 wagos goes to pump. The other black in with orange is the the R on the plug... does that make sense...

 

[ShaunCorbs]

Good is the nest new and set up for a two / y plan system eg when hot water is off the grey is live to the port valve ?

 

[Murdoch]

Why have you got a black not connecting to anything? Where does it come from

 

[E45Y123]

Why have you got a black not connecting to anything? Where does it come from

The black the at the top on it's own, then the grey in the next one down is for the hot water. But I have disconnected the cylinder stat.

 

[E45Y123]

Good is the nest new and set up for a two / y plan system eg when hot water is off the grey is live to the port valve ?

The nest is new (a week old but just got round to fit it...) and yes all wired from y plan diagram...

 

[ShaunCorbs]

Have you tested with a multi meter at the valve wago ?

 

[E45Y123]

Have you tested with a multi meter at the valve wago ?

So at orange, bottom right wago. I have 240v with heating and hot water off.

 

[E45Y123]

So at orange, bottom right wago. I have 240v with heating and hot water off.

But if I press the button on the heat link to manually override the system it drops to 30ish volts...

 

[ShaunCorbs]

Now try turning the heating on via the app ?

 

[E45Y123]

Now try turning the heating on via the app ?

That then overrides the manual mode and I'm back to a boiler that is constantly calling for heat and no control at the stat...

 

[ShaunCorbs]

Unwire the nest eg load side eg 3,4,6

Then with your multi meter do you have voltage on 3 and 6 ?

 

[E45Y123]

Unwire the nest eg load side eg 3,4,6

Then with your multi meter do you have voltage on 3 and 6 ?

Thanks for the reply, I will check when I'm home and let you know.

 

[E45Y123]

Unwire the nest eg load side eg 3,4,6

Then with your multi meter do you have voltage on 3 and 6 ?

Hi, I have checked for voltage across terminal 3 and 6 and i have 240v across each...

 

[ShaunCorbs]

It’s the stat either config/ set up wrong or it’s broken when everything is off heating and hot water 3 and 6 should be 0v

 

[E45Y123]

It’s the stat either config/ set up wrong or it’s broken when everything is off heating and hot water 3 and 6 should be 0v

That's what I originally thought... I think it may have been returned to the shop... not sure but it didn't looked packed in the box properly when I opened it but didn't think anything of it...

Thank you for your help! It is very much appreciated!

I will return it to the shop and exchange for another one... fingers crossed that one works...