Drayton LP711 to Nest 3rd Generation

[bishbasher]

I am trying to replace a British Gas UT2 (which google tells me is a rebadged Drayton LP711 single channel controller) with a Nest 3rd Generation Heatlink (HL) and stat.

I've used the excellent resources on this forum to get me so far, but have hit the limits of my abilities and would appreciate some advice. A mans got to know his limitations....

Picture of the controller wiring before any works:

IMG-2774

• bishbasher
• 5 Jan 2020

The existing British Gas RS1 stat, along with wiring to the boiler are both terminated here.
I have wiring to N L 1 3 4.

Firstly I have disconnected the wiring for the old stat from the controller.

This leaves:

N & L - I have single wires into each, coming from a separate fused 240v feed to the controller.
3 - Hot Water (HW) ON
4 - Central heating (CH) ON

The wire that was in 1 came from the disconnected stat.

So, I have disconnected the N & L from the old controller wiring and used these to power the Nest HL.
Wire 3 (HW) has been connected to HL 6 (Call for Water)
Wire 4 (CH) has been connected to HL 3 (Call for Heat)

I have connected the Nest stat to T1 and T2 on the HL and this is powered and configured.

So far so good.

Now if I test at this point in the install I have hot water working but no heating. I'm triggering the heating by turning up the stat (there's an audible click) but I've tried also pressed the button on the front of the HL. I wasn't actually expecting anything to be working at this point, as I haven't jumpered the live feed on the heatlink to ports 2 and 5.

When I connect the L on the HL to 2 and 5 I get no change in behaviour. Here's what it looks like.

IMG-2778

• bishbasher
• 5 Jan 2020

IMG-2780

• bishbasher
• 5 Jan 2020

Troubleshooting.
If I disconnect the HL 6 Call for Water, leaving HL 3 Call for Heat there's no change.
Now for no real purpose, if I now disconnect HL 3 Call for Heat and replace it with the wire that was in HL 6 (Call for Water) I get both heating and hot water, I think together. The boiler is successfully triggered by the stat for heating.

My understanding of the ports on the HL ports 1-3 (HW) is that the live feed presented to port 2 will be connected to port 3 when ON and connected to port 1 when OFF. Ditto for ports 4-6 (CH). I have also observed that if I twist together wires in 2 (L) and 3 (Call for Heat) this doesn't however trigger the boiler CH.

I've had a look at the wiring terminated in the boiler and observed that the black wires terminate on LR and the grey wires on LSW. I can post pics of this end if useful.

That's all I've got. Along with a bit of a cold house and that particular type of understanding look on my wife's face

All help and advice appreciated.

 

[ianmcd]

I am trying to replace a British Gas UT2 (which google tells me is a rebadged Drayton LP711 single channel controller)

Completely wrong the UP2 is a twin channel programmer and the LP711 is a single channel time switch so it will have to be wired as an LP722,
your existing wiring has a connection at terminal 1 which is HW off so means you have a Y plan system, so you have wired it completely wrong, you need to trace the wire in terminal 1 origionally and connect it to terminal 4 on the heat linkk

 

[bishbasher]

Hi Ian
Thanks for your reply I appreciate that. I wasn't sure if I was on an S or Y plan - now i know.

I labelled the wires before disconnecting anything from the original controller. So I understand you're saying that I may be missing a wire on terminal 4 of the heatlink, and this will be the wire that was originally connected to terminal 1 on the old controller.

The wire that was in terminal 1 (HW off) goes back to the old stat, which is completely disconnected i.e all wires removed? I have traced the cable back to confirm this, as it's not far from the boiler.

Many thanks

 

[ianmcd]

Hi Ian
Thanks for your reply I appreciate that. I wasn't sure if I was on an S or Y plan - now i know.

I labelled the wires before disconnecting anything from the original controller. So I understand you're saying that I may be missing a wire on terminal 4 of the heatlink, and this will be the wire that was originally connected to terminal 1 on the old controller.

The wire that was in terminal 1 (HW off) goes back to the old stat, which is completely disconnected i.e all wires removed? I have traced the cable back to confirm this, as it's not far from the boiler.

Many thanks

it will still need to be connected from the heat link to the 3 port valve

 

[stem]

The existing programmer is removed and all of the wires terminated at it are transferred over to the Nest Heat link terminals that have exactly the same function, as per below:

In addition links are required between the Heat link (L) and the two 'Common' terminals (2) and (5) so that all three terminals are electrically connected together.

Any existing room thermostat (if fitted) should be decommissioned to stop it interfering with the Nest. It can't just be disconnected, otherwise the heating wiring would be left permanently 'open circuit' and not operate. This is done by tracing the old thermostat cable back to its origin. Note where the wires in the cable are terminated and disconnect all of them. Then insert a link to join together the terminals where the thermostat's two live wires (Live and Switched Live) have just been removed from. All thermostats are different, but there should be a diagram printed on it that will identify these wires. As a temporary measure, the existing thermostat could be left in place and set to its maximum setting

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

 

[ianmcd]

The existing programmer is removed and all of the wires terminated at it are transferred over to the Nest Heat link terminals that have exactly the same function, as per below:

View attachment 180357

In addition links are required between the Heat link (L) and the two 'Common' terminals (2) and (5) so that all three terminals are electrically connected together.

Any existing room thermostat (if fitted) should be decommissioned to stop it interfering with the Nest. It can't just be disconnected, otherwise the heating wiring would be left permanently 'open circuit' and not operate. This is done by tracing the old thermostat cable back to its origin. Note where the wires in the cable are terminated and disconnect all of them. Then insert a link to join together the terminals where the thermostat's two live wires (Live and Switched Live) have just been removed from. All thermostats are different, but there should be a diagram printed on it that will identify these wires. As a temporary measure, the existing thermostat could be left in place and set to its maximum setting

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

The wire that was in terminal 1 (HW off) goes back to the old stat, which is completely disconnected i.e all wires removed?

will need to be connected to the mid position valve

 

[stem]

The wire that was in terminal 1 of the existing programmer would have been connected to the 3-port valve for the original programmer to have worked.

 

[ianmcd]

The wire that was in terminal 1 of the existing programmer would have been connected to the 3-port valve for the original programmer to have worked.

Yes I know but if you read it he has totally disconnected this wire now

 

[stem]

Yes exactly. As you had already informed him that he needed to put it back in the post before mine, I didn't see the need to mention it again.