Replacing Altech ALTHC001 Controller with Nest 3rd Gen

[ianmcd]

The white wire is terminal 5. You said terminal 4... so I did terminal 4 - see picture 1?
I guess you meant N+4, then N+5, then N+6?
If I knew what I was doing I wouldn't be asking chap.
Give me 2 mins and I will update.

read the post i said AT THE NEST

 

[agwright99]

read the post i said AT THE NEST

At the nest, all are 240v.

 

[ianmcd]

Then the nest is fine the problem is else where, what are you getting between white and N

 

[agwright99]

White (from the Valve) to N is nil

 

[ianmcd]

what reading do you get between the White wire and the earth wire ?

 

[agwright99]

what reading do you get between the White wire and the earth wire ?

240V

 

[ianmcd]

OK you have lost the Neutral supply somewhere

 

[agwright99]

...
There is some wiring behind the controller which includes a loose connection (third picture attached). This might be the issue as I could have knocked it. The grey wire from the boiler I guess is a live return(?) and connects to the red control wire which I think goes to the valve(?) via the circuit box. The yellow seems deliberately blanked off and appears blanked in the circuit box (top right). The light blue looks like it might have been attached to something behind the controller. In the circuit box I think this joins another light blue in junction 2 - which seems to connect to a dark blue wire from the valve and a black wire from another cable (which seems to be a mains type cable).
...

Could it be this one from behind the controller...?
Picture attached - pointing at it with black probe
EDIT: testing neutral from the nest to this one is 240v, earth to this one is also 240v

 

[ianmcd]

EDIT: testing neutral from the nest to this one is 240v, earth to this one is also 240v

That means that wire is live if you are doing it correctly, switch the heating and HW off and measure it again

 

[agwright99]

That means that wire is live if you are doing it correctly, switch the heating and HW off and measure it again

Assuming I’ve done it correctly for now. Measuring it with the HW/CH on/off doesn’t seem to make a difference.
Doesn’t sound safe to have a live wire knocking about in the junction box but that aside could it be the issue? The only thing it could reasonably connect to in there is the grey wire from the boiler (the live return?) as it wasn’t connected to the Altech previously.

 

[ianmcd]

No it isnt safe put it into a terminal block and insulate it

 

[agwright99]

No it isnt safe put it into a terminal block and insulate it

Ok will do. Not the answer to missing neutral supply though... any idea where I might start looking or what could be wrong?

 

[ianmcd]

The N at the nest is working so see where that connects to, the only other light blue wire I can see in your pics is in the existing room stat, is that conneceted to anything ?

 

[agwright99]

The N at the nest is working so see where that connects to, the only other light blue wire I can see in your pics is in the existing room stat, is that conneceted to anything ?

The neutral at the nest comes out of the boiler (with live, earth and a grey wire I guess is live return. This last one goes to a red wire in the circuit box).
The light blue wire in the old room thermostat box is live but in a terminal block isolated off.
There is another cable joining the circuit box which has a black wire going to the same terminal (2) but I don’t know where that comes from. it might join the conservatory system since it runs off in a different direction but I didn’t think that system touched this one.

 

[ianmcd]

The light blue wire in the old room thermostat box is live but in a terminal block isolated off.

Why is it Live ?