Nest 3rd Gen Wiring Question

[Colm C.]

I want my new 3rd Gen. Nest to control both a heating zone and the boiler itself so that I can remotely switch it on/off. The heating is working fine (terminal 3 comes live as the heatlink calls for heat) but terminal 6 on the Heat Link is permanently live and does not switch when selecting Hot Water on/off in the app. I followed the wiring instructions (see photo). Have I got it wrong? Thanks in advance.

 

[ianmcd]

Nope that is completey wrong you need more cables

 

[picasso]

You have nothing connected to 3 on the heat link so that's not controlling your heating and nothing connected on six so why would you expect it to control your hot water ? what are you trying to control, combi, zone valves or ?

 

[Colm C.]

I was just testing my wiring before I installed the heat link and thermostat properly. I was testing terminal 3 and 6 with a phase tester. Terminal 3 will be connected to my heating zone pump and I was intending to connect terminal 6 to the boiler but I was surprised to find that terminal 6 was permanently live regardless of whether the HW was on or off in my App.

 

[picasso]

Probably just ghost voltage, what type of system do you have , its unusual to control the boiler on/off using the hot water on side of the nest.

 

[Colm C.]

I have a Grant Vortex Condensing Boiler connected to a Systemlink manifold with 4 heating zones (two of which have Nest thermostats connected). I want the new Nest to control the third heating zone and the HW control in the app to switch the boiler ON/OFF. I want to be able to remotely turn on the boiler/heating. Once the boiler is ON it heats a separate HW cylinder. I was hoping to get some direction on the correct wiring for terminals 4,5 & 6

 

[picasso]

How is the hot water cylinder plumbed in ? is there a separate pump and circuit off the systemlink or plumbed straight off the boiler?

 

[Colm C.]

How is the hot water cylinder plumbed in ? is there a separate pump and circuit off the systemlink or plumbed straight off the boiler?

It's pumped straight off the boiler to both the CH manifold and the HW cylinder.

 

[picasso]

Can you post a pic or drawing ?

 

[Colm C.]

Probably just ghost voltage, what type of system do you have , its unusual to control the boiler on/off using the hot water on side of the nest.

I decided to connect a light bulb to Terminal 6 and the Neutral terminal and the light only came on when I had the HW schedule set to ON. Your theory about a ghost voltage was correct! Many thanks for that. I'm now good to go. I didn't want to undo the existing system until I was confident the 3rd Gen Nest would work as I hoped. Now I am, so again thanks for your patience.