Wiring centre not as per Y plan diagram

[Scatts570]

I'm getting ready to fit a new 3rd generation Nest thermostat (and Heatlink). When I've looked at the wiring centre it doesn't look like any wiring diagram. There are no wires to positions 1,2,3,4 & 5. There are connections to positions 6, 7, 8, 9 & 10 with permanent lives on 11 & 12.
The issue I have is that when I look at Y plan wiring diagrams they're all consistent with 1 being live and 2 being neutral and so on.

I'm assuming that I now need to trace all the wires to try and find the correct positions for the call for heat and call for hot water. (I also want to disconnect the programmer, but don't know which wires are which yet).

Should all wiring centres be wired up consistently or do electricians tend to wire up for convenience? I.e where the wires fit closest.

Also, the wiring centre box lid refers to a 2 port valve, but I have a 3 port (diverter). Should the boxes be replaced if The system has Been changed.

 

[petit_pablo]

hahahaha - welcome to our world!
Heating wiring is a as per someones whim quite often.

Put a picture up and we can see if its decypherable.

 

[Scatts570]

Pics attached

 

[petit_pablo]

It looks like 6 is HW off, 8 is HW on and 9 is CH on.

From that you should be able to trace which cables are for the programmer, room stat and HW cylinder.

 

[Scatts570]

Thanks Pablo,

I worked out that 6,7 & 9 go to the valve (diverter).

7 & 10 got to HW tank (assuming cylinder thermostat)

8 goes to the pump.

I'm assuming the red live 12 is one wire from boiler and one wire to the programmer.

The other wires go off either into the wall or through the floor.

Oh well, break out the bell wire and fluke and tell my missus there's no heating for a few hours while I figure it out.

 

[D_Hailsham]

The links between terminals, specified by the Drayton, are missing; so the result is a cobbled together system. It's so much easier if links are in place and wires connected to the appropriate labelled terminals.

Info above the numbers 1 to 16 are for S Plan; below is for Y plan (aka biflow)

The installation manual is here

If you boiler has pump overrun, and the pump is wired via the wiring centre, you need to make the following change:

Link 12 to 14
Connect pump live to 13; and connect 13 to the pump L terminal on the boiler.

 

[Terrywookfit]

All that room yet they still make a Rats nest with the fookin wiring.

 

[Scatts570]

Do I need to wire the Heat Link directly into the wiring centre? Or can I replace the Drayton LP722 programmer with the Heat Link. I'm assuming I should be able to utilise the live, neutral, call for heat and call for HW. (With a daisy chained link on the Heat Link between the live, common Heat and common HW)

Sounds a lot simpler than messing around trying to trace what wires are what.

 

[Scatts570]

This is what I'm thinking if I replace the Drayton LP722 programmer with the Nest Heat Link:

 

[stem]

Very good, except for the unnecessary link from 'L' to 'Hw off' and 'Ch off' at the Drayton. The Drayton has its links made internally, as can be seen above. On the Nest you have to install them (L and the Commons 2 & 5) as you have correctly shown.

Don't forget you will need to remove the existing wired thermostat and then connect the wires that went to its 'live' switching terminals together.

The Nest thermostat also requires a 12V supply which can be wired to the Heatlink T1 & T2, or a separate plug in power supply.

 

[Scatts570]

Thanks for the advice.

The thermostat 12v wires are an issue as the wiring centre is upstairs in the airing cupboard, the programmer is on a far wall in the kitchen and the thermostat is in the hallway. If I replace the programmer with the Heat Link I'm not going to be able to run wires to a suitable place in the house (lounge) to provide power to the thermostat.

I'm going to have to have the slightly less integrated look of having the Nest plugged into the wall socket and use Wi-Fi.

Just a query, but why do I need to connect the wires going to the old thermostat together? Ca I not just remove them from the wiring centre end? (or is it easer to short circuit them?)

 

[stem]

If you don't connect them together, then you will have a permanently open circuit and the heating will never come on. It would be the same condition as you have now when the thermostat is off. (i.e up to temperature)

By joining the live switching wires together, the old system will be bypassed and the Nest will now take control via the Heatlink. You can link the terminals where the thermostat wires are presently connected at the wiring center if you prefer. That's what I was trying to explain earlier. But you do have to insert a link where the thermostat switching wires were connected, you can't just remove the thermostat wires and leave it open circuit.

BTW, I believe that the Nest Thermostat still uses Wi-Fi to communicate with the Heatlink even if it's powered by it.

 

[Scatts570]

Many thanks Stem.

That all makes sense now.

I'll pick a suitable early morning once the house has warmed up with a tank of hot water. Have the camera on my phone ready, a heating engineer's phone number just in case, flick that circuit breaker off and make a start. This Friday's looking good.

Cheers everyone

 

[D_Hailsham]

7 & 10 got to HW tank (assuming cylinder thermostat)

A Y Plan needs three wires from the cylinder stat (common, call and sat). The earth wire may have been used as one of the three wires.

HW Off, cylinder stat sat and the grey wire of the valve need to be connected together for CH only to work.

 

[stem]

D Hailsham is right, I assumed that you don't have a 'Y Plan' because you haven't shown a wire going to 'HW off' on your Drayton LP722 diagram.

You may have a 'S Plan' which has two, 2 port motorised valves instead of one, 3 port and that set up doesn't need the 'HW off'. Best to check now before you start work.