HELP! New Nest Gen3 with Old System?

[duckdodgersuk]

Hi There,

I picked up a Nest Gen3 Thermostat in the Black Friday sales but am having a nightmare installing it with my old Glowworm Ultimate 40ff system boiler.

Old Thermostat

The Hot Water Tank is upstairs along with the LWC1 wiring station and Drayton LP241 programmer.

Drayton LP241 programmer

The inside of the LWC1 wiring station doesn't match any of the wiring diagrams on the drayton website : https://www.draytoncontrols.co.uk/installers/training-centre/wiring-diagrams
You can see it also has a overrun pump PCB and i'm not sure how to wire this with the Nest Thermostat?

LWC1 wiring station

I don't mind paying to get it installed correctly, but Even the Nest Engineer was scratching his head and left. He even tried to charge me for the visit!

Please help.

 

[ericmark]

Looking at the tank it seems the boiler heats the tank then the tank runs the central heating, this means the boiler switches on/off but the radiators can be modulated so low hysteresis.

It seems likely Nest can replace the LP241 programmer, normally one would try to re-use the thermostat wires, but in your case I think I would just bridge L to 3 (call) as tracing wires other end may not be easy.

Not sure what the small circuit board does.

Wait and see if any better answers.

 

[CBW]

Are you wanting to control the hot water with the Nest, or just the heating?

 

[duckdodgersuk]

I’m looking to Control both if possible

 

[stem]

The wires now going to the Drayton LP are connected as follows:

They are moved from there to the Nest Heat link terminals that have exactly the same function. So, for example the wire in CH ON (4) will move to Heat link 'Heating Call For Heat' (3), and the wire in HW ON (3) will move to Heat link 'Hot Water Call For Heat' (6) Only the wires that are presently there need to be moved, so don't worry if some terminals are vacant.

A link is required between (L) and the two 'Common' terminals (2) and (5) so that the 3 terminals are electrically connected.

The old thermostat needs to be decommissioned. It can't just be disconnected. This is done by tracing the old thermostat cable back to its origin. Note where the wires are connected and disconnect them. Then insert a link to join together the two terminals that you have just removed the thermostat wires that used to go to the (L) and (3) terminals of the thermostat from so that they are electrically connected.

If this is difficult to do, as an option, the old thermostat can be left in place and the wire in (3) moved into terminal (L) with the other wire already there.

The Nest thermostat can be powered using a separate plug in power supply, or by connecting the Thermostats T1 & T2 terminals to the same terminals at the Heat link.

 

[duckdodgersuk]

The Nest Thermostat should wire in to the old wall socket fine as long as its 12v.
Its just the Wiring Station that I need help with.

 

[stem]

Once the old thermostat cable has been disconnected as I explained earlier, so that is is not connected to anything at either end, then you can then use it to connect the Heat link T1 & T2 terminals to the Nest thermostat T1 & T2 terminals.

If by "wiring station" you are referring to this:

You only need to trace the room thermostat cable back there and carry out what I described earlier:

Note where the wires are connected and disconnect them. Then insert a link to join together the two terminals that you have just removed the thermostat wires that used to go to the (L) and (3) terminals of the thermostat from so that they are electrically connected.

If you take the second option:

If this is difficult to do, as an option, the old thermostat can be left in place and the wire in (3) moved into terminal (L) with the other wire already there.

Then you don't need to do anything in there at all. You won't of course be able to use the existing thermostat cable for connecting T1 & T2, because it will still be connected to 230V

I'm a bit worried about the state of the existing wiring though, there seem to be wires that aren't secured or even enclosed in a sheath leaving the wiring centre. You would be well advised to get a pro in to sort it out properly.

 

[duckdodgersuk]

This is what Drayton sent me ? But still doesn't match my wiring centre?

 

[stem]

I would be surprised if it did, much depends on the personal preferences of the original installer. If it's working correctly, the wires will be going to the right places, but could be using different ways to get there.

Do you know what the PCB in there is for?

 

[duckdodgersuk]

The PCB is a pump overrun 408401. This keeps the pump running for 4-6 minuets after the boiler is off to prevent over heating
"A feature that some boilers require, pump overrun is when the boiler pump continues to run after the boiler has finished firing. This allows the boiler to dissipate excess heat by creating a flow of water through it for a short period of time once the burner is off." https://www.pactrol.com/pdfs/Pactrol_POR_Pcb.pdf

 

[ianmcd]

Do you know what the PCB in there is for?

@stem that is not a HW Cylinder it is a thermal store so no zone valves and no end switches hence the PCB

 

[stem]

I could see it's a thermal store, but I've never seen the relay located in a Drayon wiring centre before though. Are they supplied like that by Drayton? I don't like its close proximity to the mains terminals.

OP, it doesn't make any difference to installing the Nest Heat link though, you are just exchanging a Drayton LP programmer which simply contains two 'on & off' switches, one for heating and one for hot water for a Heat link that also contains the exact same thing, so you are swapping like for like.

 

[ianmcd]

I could see it's a thermal store, but I've never seen the relay located in a Drayon wiring centre before though. Are they supplied like that by Drayton? I don't like its close proximity to the mains terminals.

OP, it doesn't make any difference to installing the Nest Heat link though, you are just exchanging a Drayton LP programmer which simply contains two 'on & off' switches, one for heating and one for hot water for a Heat link that also contains the exact same thing, so you are swapping like for like.

Not sure if the pcb comes like that mate have never seen one, cant understand why the programmer with a HW on or off has been fitted as there is no electrical control over the HW it simply passes through and induction coil and picks up its heat, it doesnt have any pump or valves to be controlled electrically

 

[stem]

Doh! yes of course that basic fact slipped the ol grey matter . Of course the store is permanently hot, and generates instant hot water for the taps, it was the use of the 2 channel programmer and the diagram of the Y-Plan that the OP posted that had lodged in my brain.

Perhaps the hot water channel is being used to control the boiler, so that it can be switched off during holidays, or for a few hours during the night when there isn't any demand just in case it happens to come on due to natural heat loss and might wake folks up.

 

[ianmcd]

Doh! yes of course that basic fact slipped the ol grey matter . Of course the store is permanently hot, and generates instant hot water for the taps, it was the use of the 2 channel programmer and the diagram of the Y-Plan that the OP posted that had lodged in my brain.

Perhaps the hot water channel is being used to control the boiler, so that it can be switched off during holidays, or for a few hours during the night when there isn't any demand just in case it happens to come on due to natural heat loss and might wake folks up.

yes thought of that too mate then seen that the OP had the LP set at timed, I would have thought it should be set to Gravity and constantly on,so the boiler and the primary pump were always on and controlled by the Cyl stat, wont argue with anyone as I have never seen that set up, more than happy to be educated