Nest 3rd generation Thermostat and C-Plan system

[D_Hailsham]

Thanks for your help, so if i change the dip switches on the programmer to fully pumped it will work although the water is gravity fed?

If the motorized valve has six wires and the system is wired as in your diagram then, yes, you can set the dip switch to fully pumped and you will then be able to have separate CH and HW times.

I converted the gravity/pumped system at my last house to C Plan over 20 years ago with the programmer set to fully pumped and it worked fine.

 

[abel88]

Cheers, i will check the wiring and see if that'll work. If it is the case, would wiring to the Nest stat be straightforward as in my 1st post, what about the common terminals on the Nest? Will these need to be connected as i only have 2 wires going to my current programmer.

 

[D_Hailsham]

I assume you want to locate the Heat Link near the junction box and the Nest base in place of the existing stat.

How far apart will they be and are there any obstructions in the way (walls, floors etc) which could affect the signal?

 

[abel88]

The heatlink will go in the same place as the existing programmer which is next to boiler in downstairs toilet, the nest stat will be in downstairs hallway. Open plan living area so don't expect problems with signal, will onlt have to contend with a couple of closed/open doors (i get albeit low wifi signal in the boiler location)

 

[D_Hailsham]

I have edited your wiring diagram to show how the Nest should be wired.

 

[abel88]

Many thanks for that. Just to clarify: my existing wiring to my current programmer go to terminals 3 & 6(hw and ch on). Am i also to understand that i need to join terminals 2 & 5 to the live on the Nest?

Again many thanks

 

[D_Hailsham]

Many thanks for that. Just to clarify: my existing wiring to my current programmer go to terminals 3 & 6(hw and ch on).

I had assumed that your system was wired as in the diagram.

Can you identify what is connected to each terminal in your junction box? If so, post the info and I will modify the diagram.

Am i also to understand that i need to join terminals 2 & 5 to the live on the Nest?

Yes

 

[abel88]

Can you identify what is connected to each terminal in your junction box? If so, post the info and I will modify the diagram

I will try and post a picture tomorrow, it's spaghetti junction at the moment...

Many thanks

 

[D_Hailsham]

I will try and post a picture tomorrow, it's spaghetti junction at the moment.

It will help if you can separate the wires so they are not bunched together.

 

[abel88]

Success!! Changing the dip switch has allowed seperate control of HW and CH, i can't believe i've been running the same together all this time. Many thanks fopr your help again.

Regards to the wiring, i've attached a very crude diagram (the best I could do). Just a few things to note: The light gray cable in the diagram is actually white. I suspect cable 1 is the room thermostat Cable and Cable 2 is the cycliinder thermostat (only by determining where it's corresponding wire ends up connecting to on the programmer). FCU is fused connection unit. And i notice the 2 zone valve has only 5 cables not 6 (the cable directly from the valve actually goes to a junction box first which looks like it was put in to extend the cable length to the main junction box but i haven't managed to look in there to see if the 6th cable is present). Also, some pics of the mess of cabling....

Hopefully from this it can be shown how to wire the Nest base.

Thanks again for your help..

 

[D_Hailsham]

And i notice the 2 zone valve has only 5 cables not 6 (the cable directly from the valve actually goes to a junction box first which looks like it was put in to extend the cable length to the main junction box but i haven't managed to look in there to see if the 6th cable is present).

The valve needs six wires to work correctly - Brown, Blue, Green/Yellow, Grey, White and Orange.

Please check in the junction box - the grey wire is not shown on your diagram. I can't do any more until this missing wire is sorted out.

Edit: Which cylinder stat do you have; and which wire goes to which terminal? This could explain the missing grey wire

 

[abel88]

I figured i should have looked when i was sorting through this Will look tonight.

Cheers

 

[D_Hailsham]

I figured i should have looked when i was sorting through this Will look tonight.

Cheers

That may not be necessary. See my edit post above.

 

[abel88]

OK, will still have to look later. Many thanks.

 

[D_Hailsham]

OK, will still have to look later. Many thanks.

It's not just a wire missing! The whole system does not follow the C Plan wiring. (Ignoring terminal numbers.)

It would be safer, for the moment to turn the programmer back to gravity

Which pipe is the motorized valve in? It's important