Nest Again Sorry

[billsy]

I want to replace my British Gas UP2 programmer (Drayton LP822) with a Nest jobby. Did a quick compatibility check on the nest sight and none of the Drayton pin idents are listed on the checker. Drayton idents that are connected are N,L,1,3,4. Am I looking in the right place?

Many thanks

 

[Daveydub]

 

[billsy]

Yes that's the layout I currently have. I'm not sure how that correlates to the nest tho

Thanks

 

[stem]

The wires should move from the terminals of the Drayton, to the Heat link terminals that have exactly the same function. Don't worry if they don't all have a wire in, but the wires that are already in place go to the appropriate terminal at the Heat link.

The terms used by the two devices aren't exactly the same, so Here's a translation for you:

Drayton N = Nest (N)
Drayton L = Nest (L)
Drayton 1 HW off = Nest Hot water satisfied (4)
Drayton 2 CH off = Nest Heating satisfied (1)
Drayton 3 HW on = Nest Hot water call for heat (6)
Drayton 4 CH on = Nest Heating call for heat (3)

You will also need to link together Heat link terminals (L) (2) & (5) [the Drayton has these links made internally so doesn't need them]

Finally if you have an existing room thermostat, it will either need to be set to 'maximum' to prevent it interfering with the operation of the Nest, or preferably decommissioned properly by removing it and bridging the live switching terminals.

 

[billsy]

Stem
Thanks very much for that. The nest stat will replace the old room stat so I guess I can re-purpose the red and blue wires going to the old stat for the 12v nest stat supply. The other end will be connected to T1 T2 at the heat link module (12v). It that correct?

 

[stem]

Yes, you can do that. Once the existing thermostat cable is completely disconnected, it can then be re-utilised to connect T1 & T2 at the Heat link, to T1 and T2 at the Nest thermostat.

Often though the other end of the cable from the thermostat ends up at a location away from the Heat link, so it may end up being easier to run a new cable.

 

[mankey]

Apologies for butting in, but I've been looking to check just the same thing. For a system boiler I'm about to replace a Drayton LP522 & RTS1 thermostat with a Nest and have pretty much worked worked out the connections. Luckily they're exactly the same as the ones you've given.

Stem, Can I just ask one question though? My LP522 backplate isn't wired at all for CH OFF on connection 2. I assume there's nothing I need to do about this on the Nest, apart from the additional live connections and take care of the existing thermostat. I'm fitting the Nest in the same position as the RTS1.

I've established that I can disconnect the thermostat cables from the ACL LWC1 connector wiring block in our airing cupboard and re-use them for the 12v supply. I'll use the Nest 12v adapter to do that.

I'm chuffed I've stumbled across this - many thanks for your help.

 

[stem]

My LP522 backplate isn't wired at all for CH OFF on connection 2.

Don't worry, that's the same as 99.99% of heating systems. I would be surprised if anything was connected to it.

The Nest power supply comes with a small USB type connector that plugs directly into the Thermostat, like a mobile phone charger. Unless it's changed recently. I don't think it has the possibility to be wired into T1 & T2

 

[mankey]

The Nest power supply comes with a small USB type connector that plugs directly into the Thermostat, like a mobile phone charger. Unless it's changed recently. I don't think it has the possibility to be wired into T1 & T2

Thanks for the quick response. Unfortunately there won't be any spare wiring from the programmer that I can use to connect to T1 & T2 on the Heatlink so my plan to power the Nest was to re-use the cables that go to the existing thermostat. I had the Nest stand free so I was going to spur to a 3-pin socket in our airing cupboard and plug the Nest adapter in to that to supply 12v but it looks like a bit of a faff because I can't easily connect to the USB.

Cheers

 

[billsy]

Electrician here now installing nest. We have no voltage at T1/T2 on Heat Link module any ideas? Urgent reply needed please.

 

[stem]

Are you saying that with 230V power to the Heat link N & L that you are reading the voltage between terminals T1 & T2 with a multimeter and there isn't 12V DC present?

 

[billsy]

thats correct yes

 

[billsy]

I mean thats what we got. Not correct

 

[stem]

In that case it sounds like the Heat link is faulty. When its powered up it should provide the 12V at those terminals.

 

[billsy]

OK now we have 12v at the heat link but 5v at the nest thermostat