Nest 3rd gen Install on a Y-plan system

[Chris86]

Hi all,

I’m wondering if someone would be able to give me advice on how to install the NEST Thermostat (3rd Gen).

Current setup:

• Worcester Greenstar Boiler
• Drayton LP522 programmer
• Drayton RTS1 thermostat

It’s all wired up onto an Y-plan system controlling, both, the CH and HW.

I'm faily confident on installing the heatlink using the existing wiring from the programmer, my concern is mainly in regards to decomissioning the RTS1 thermostat.

I'd appreciate it if someone could cast an eye over my thoughts initally on the heatlink wiring and then advise me the wiring for the thermostat.

Programmer wiring

N = 3 x cables into N on the heatlink
L = 2 x cables into L on the heatlink
1 = HW off cable into 4 on the heatlink
3 = HW on cable into 6 on the heatlink
4 = CH on cable into 3 on the heatlink
Bridge L into 2, 2 into 5 on the heatlink.

Would this be a correct setup?


Thermostat

I'd like to decommission the thermostat and use the nest via usb mains power. I've traced the thermostat cable back to my airing cupboard and into the junction box. It consists of three cables:

• Blue = N
• Brown = L
• Earth = Call for heat (I think?)

Junction Box

Thermostat wiring in the junction box is the following:

• N (Blue) is in terminal 2
• L (Brown) is in terminal 4
• Earth (Yellow/Green) is in terminal 5

From the research I've tried to do before posting this tells me that I'd need to close the circuit if I disconnected the three cables from the junction box. I've tried to study the wiring but I can't grasp if/what wires I'd need to move. Would someone be kind enough to tell me please?

Just to note - should the white cable on the 3 port valve (terminal 4) really be wired to the 'call for heat' (by it's self on terminal 5) from the thermostat?
Since I moved into the proerty 6 years ago, I've had to manually switch the heating on and off via the programmer - it doesn't switch off once the correct temp is achived. Thinking about it and looking at the wiring in the junction box, this suggests the thermostat is being bypassed already?

Should the correct setup should be white cable for 3PV (Terminal 4) wired into Terminal 5 - call for heat? Then when I remove the thermostat, move 4 into 5 or vice versa to complete the circuit?

I'm a novice at heating system so I could be talking nonsense!

 

[Chris86]

Any help is much appreciated.
Chris

 

[Johnmdc]

All of what you say connection wise to the heat link is correct.
As you also say the thermostat has already been bypassed, for it to have worked correctly the white wire should have been in terminal 5.
So all you need to do is disconnect the 3 core flex to the thermostat and leave the white wire where it is.

 

[Chris86]

All of what you say connection wise to the heat link is correct.
As you also say the thermostat has already been bypassed, for it to have worked correctly the white wire should have been in terminal 5.
So all you need to do is disconnect the 3 core flex to the thermostat and leave the white wire where it is.

That's reassuring Johnmdc. Many thanks for taking the time to look through my post.

Cheers,
Chris

 

[Johnmdc]

No probs.