Drayton LP241 to Nest 3rd Gen Help

[p2ddy]

We've just moved into a new house and are hoping to upgrade the existing system to Nest. I've read through some previous forum messages with similar system upgrades but thought I'd reach out to get some specific clarifications from experts out there before attempting the job - last resort would be to get someone out to install if it simply is beyond my capability but hoping its not.

The Nest will replace a Drayton LP241 Programmer and a Wiring Centre located in the upstairs Airing Cupboard and a wall mounted Honeywell T6360B Thermostat located downstairs in the entrance hall.

The plan is to replace the Drayton Programmer with the Nest Heat Link and switch the Honeywell Thermostat out for the new Nest one using the existing wiring from the Wiring Centre to provide the 12V power by connecting it to the Heat Link (this is what I have gleamed is the best way forward from other posts!).

I've attached photos of each of the three boxes (outside and inside).

Drayton Programmer:


Wiring Centre:


Honeywell Thermostat:


Your experience, help and advice will be very much appreciated!!

Many thanks.

 

[ianmcd]

The Nest will replace a Drayton LP241 Programmer and a Wiring Centre

You cant replace the wiring centre, the nest receiver replaces the Programmer, and the existing thermostat you will have to join the com and NO wires, the neutral and earth wires will have to be safely terminated and insulated (terminal strip and insulation tape is fine) or removed completely from the wiring center, but if you remove the live and switched live from the stat at the wiring centre you will need to add a link

 

[p2ddy]

Thanks @ianmcd! Apologies for my ambiguous mission statement, you are very correct, i had planned on keeping the wiring centre and just replacing the Drayton programmer in the airing cupboard. Can you elaborate more on removing the live and switched live from the wiring centre for me? I think (hope) changing out the Drayton box should be fairly straightforward, more concerned about switching out the Thermostat and and changes required in the Wiring Centre, particularly to get 12V power back to the Nest Thermostat. Thanks again for your help!

 

[ericmark]

In the wiring centre the only wires where you can be sure colour is correct is the cable to the motorised valves which have an orange wire so you can see which two cables are from motorised valves in your case the black pair slightly right of centre. It seems the brown goes to 4 and 8 so one of those connects to the tank thermostat and the other the wall thermostat.

8 seems to connect to 14 which seems to go to one of the white cables which I would guess goes to tank thermostat so it seems likely 4 connects to wall thermostat. So likely 2 and 3 go to wall thermostat.

I am trying to go through my reasoning process so you can check if I am correct. But my copy of S plan is clearly not using same connections in the wiring centre as yours

and what you need to do is using logic work out what each wire does.

 

[p2ddy]

Hi @ericmark, thanks for your input! You are very correct about the orange cables going to the motorised valves! Can you explain your logic as to why 4 would connect to the wall thermostat?! I do agree though (although not teste yet) that 2 and 3 connect down to the wall thermostat in the entrance. Will the blue and earth feeds to the thermostat also run from the wiring centre (four cables total at the thermostat)?

 

[Terrywookfit]

4 must connect to Room stat as it energises the heating valve ….Live on brown opens the valve.

 

[ericmark]

The diagram shows brown on motorised valve goes to the thermostats.

 

[stem]

As I think you have figured the Nest Heat link replaces the existing programmer. The wires are moved from the programmer to the Heat link terminals that have exactly the same function. So, the wires in:

Drayton LP241 N = Nest N

Drayton LP241 L = Nest L

Drayton LP241 3 'HW On' = Nest 6 'Hot water call for heat'

Drayton LP241 4 'CH On' = Nest 3 'Heating call for heat'

Drayton LP241 Earth = Nest Earth

Links now need to be added so that the Nest Heat link terminals L, and the 'commons' 2 and 5 are all joined together.

1. You now need to find the other end (origin) of this cable at the room thermostat.

2. When you find the origin of the cable, note where the wires from the thermostat terminals 1 (Brown wire) and 3 (Black wire with brown sleeve) are connected.

3. Disconnect and remove the Honeywell Room thermostat.

4. Disconnect all of the wires from the thermostat cable at its origin, and then insert a link to join together the two terminals that the 2 wires you have identified have just been removed from. The cable should now be completely disconnected at both ends.

If the original installer has followed the lid nomenclature (caution, not all do!) it is likely that the origin of the existing thermostat wires are from the wiring centre terminals 2 & 3.

Which in your case below looks promising, but do check to be sure. If this is the case, once the brown & black wires from wiring centre 2 & 3 have been removed, you can insert a link between them, or instead simply put the two red wires at the top in the same terminal.

The wiring centre may not be close to the Heat link, so likely you may have to extend the cable to reach it.

5. Two wires in the original thermostat cable can now be used to connect T1 and T2 at the Heat link to T1 and T2 at the Nest Thermostat. Insulate the other unused wires.

 

[p2ddy]

@stem I simply cannot thank you enough for your clear and explanatory response! Absolutely amazing. Is it likely that all four of the cables from the thermostat will trace back to the wiring centre or just the ones in terminals 1 and 3?

 

[stem]

You're welcome. Just a descriptive note, there is only one 'cable' but that one cable contains four 'wires' or 'cores'

As it is the same cable, it should have the same 4 wires at each end. So yes, to answer your question. But do check to be sure. It's unlikely to be otherwise, but I once came across an installation where someone had tapped into a thermostat cable to supply a wall light halfway along its route.

 

[p2ddy]

@stem - thanks for the response again! Think I'm going to invest in a cheap tracer and give it a crack, fingers crossed I don't come across any crazy wire tapping you mentioned!! Really really helpful, thank you so much again!

 

[stem]

Like I said you're welcome. Please post back to let us know how you got on, or if you have any other questions.

 

[p2ddy]

@stem - I eventually got round to attempting to install the Nest setup at the weekend, really happy to report that it went even better than expected as there was already spare wires running between the wiring centre and heatlink so didn't even need to run a new external cable between them! Winner! Used a multimeter to isolate the existing thermostat cables and ensure that the feedback to the new nest thermostat was 12v using the old cables once the rewiring was done. Can't thank you enough for your guidance, spot on mate! Really really appreciate you taking the time to help. As an aside, I'm really happy with the Nest setup and find the digital display on the thermostat great to show a heads up of the current and forecasted weather outside and it's nice to be able to turn the heating up and down from the app on the mobile without running up and down the stairs!

 

[ianmcd]

The Nest will replace a Drayton LP241 Programmer and a Wiring Centre located in the upstairs Airing Cupboard

NO the wiring centre stays as it is