Help Replacing Drayton LP722 and Drayton RTS stat with Nest 3rd Gen

[justbigboned]

Hi all,

I hope this is the right place for my first post. I'm hopeful someone may be able to assist me.

I've just acquired a Nest 3rd Gen which I'd like to install.

The house was built in 2005 and has an Ideal Icos boiler, Drayton Lifestyle LP722 programmer and what I think is a Drayton RTS1 thermostat (not taken it off to look behind yet).

There appears to be two motorised valves in the airing cupboard near the hot water tank. One is a Drayton ZA5 (C/H) and the other a Danfoss Randall HPA2 (H/W). Since there are two valves, I'm guessing that the system is S plan.

The wiring centre is in the airing cupboard also and is a Drayton Lifestyle box.

My perhaps fuzzy logic tells me that I should be able to shut the power off, remove the wires from the LP722 one at a time, labelling them as I go, then insert them into the Nest Heat Link. I'm just not sure which wires go where and also people seem to be doing it directly from the wiring centre so my approach may well be wrong!

What I'd then like to do, is use the existing thermostat wires to power the Nest Thermostat in the same location as the old stat. The old stat is 230v AC, which doesn't seem to be suitable for the nest so I figure I have two possible options.

a) disconnect the old stat wires at both ends and use T1 and T2 (presumably a 12v supply) in the Nest heat link to power the Nest Stat with the old wires. Not sure how many wires go into the old stat though or what to do with the leftovers to terminate them.

b) use a 12v DC driver (LED light fitting type) at the stat end immediately before the connection to the Nest Stat.

I have very limited electrical and plumbing experience and I dont own a multimeter. Electrics wise, I've wired 16amp sockets, changed an MCB, various light fittings, ceiling roses and sockets but thats about it.

Am I on the right lines with the above? Is there anything I should be on the lookout for?

I'd appreciate any thoughts on the matter. It's cold and the last thing I want to do is not anticipate something and have no heating. Nest installers want £100 (3 quotes, that was middle), which may or may not be excessive and I'll go that route if I'm in any doubt.

Thanks very much in advance.

 

[stem]

You are on the right lines. The Nest replaces the LP722. The LP722 will have the connections to its terminals as shown below.

From this you can identify what the wires do. Not all of the terminals will have wires connected, so don't worry about this.

Mark the wires carefully and move them from the LP722 to the terminals at the Heatlink that have the same function. [For example 'HW on' (terminal 3) at the LP722 = 'Hot water call for heat' (terminal 6) at the Heatlink.] If there is more than one wire in some of the terminals, they will need to be moved together.

Once all of the wires are moved across, insert wires to link together the Heatlink terminals Live (L) and the two Commons (2) and (5)

The existing room thermostat will need to be decommissioned to prevent it will overriding the Nest, and it can't just be disconnected, otherwise the heating wiring will be 'open circuit' and not operate. This can be done by tracing the wires back from the thermostat and finding where they originate from. Then disconnect them at their origin, and the two terminals where the switching wires came from should be joined together. If yours is an RTS1, the switching wires will be connected to terminals L and 3. Any neutral, if present can just be disconnected.

Once the original thermostat cable has been completely disconnected you can use 2 of the cores to connect the T1 & T2 terminals of the Heatlink to terminals T1 & T2 of the thermostat. However, often the cable runs from the thermostat to a wiring centre usually in the airing cupboard and may not be near the Heatlink, meaning that it may be easier to run a new cable, or use a plug in power supply for the thermostat. I would not recommend using any power supply other than one supplied by Nest. It may not be stablised enough, or be to the correct specification. Whilst it tells you the thermostat needs 12v DC, I don't think the Nest documentation tells you the polarity.

 

[justbigboned]

You are on the right lines. The Nest replaces the LP722. The LP722 will have the connections to its terminals as shown below.

View attachment 131399

From this you can identify what the wires do. Not all of the terminals will have wires connected, so don't worry about this.

Mark the wires carefully and move them from the LP722 to the terminals at the Heatlink that have the same function. [For example 'HW on' (terminal 3) at the LP722 = 'Hot water call for heat' (terminal 6) at the Heatlink.] If there is more than one wire in some of the terminals, they will need to be moved together.

Once all of the wires are moved across, insert wires to link together the Heatlink terminals Live (L) and the two Commons (2) and (5)

The existing room thermostat will need to be decommissioned to prevent it will overriding the Nest, and it can't just be disconnected, otherwise the heating wiring will be 'open circuit' and not operate. This can be done by tracing the wires back from the thermostat and finding where they originate from. Then disconnect them at their origin, and the two terminals where the switching wires came from should be joined together. If yours is an RTS1, the switching wires will be connected to terminals L and 3. Any neutral, if present can just be disconnected.

Once the original thermostat cable has been completely disconnected you can use 2 of the cores to connect the T1 & T2 terminals of the Heatlink to terminals T1 & T2 of the thermostat. However, often the cable runs from the thermostat to a wiring centre usually in the airing cupboard and may not be near the Heatlink, meaning that it may be easier to run a new cable, or use a plug in power supply for the thermostat. I would not recommend using any power supply other than one supplied by Nest. It may not be stablised enough, or be to the correct specification. Whilst it tells you the thermostat needs 12v DC, I don't think the Nest documentation tells you the polarity.

Thanks very much for this stem. I'm going to buy a continuity tester tomorrow just to be sure I'm tracing the wires correctly. If the thermostat wires from the wiring centre arent long enough would I be ok to using a choc bloc to extend, or one of those little boxes, I forget the name of them? I'll then terminate the other wires using a choc bloc and tape.

I think I have this clear in my head now, I appreciate the reply and hopefully this will help someone else with a Drayton unit, they seem pretty common (under various brands) but I wasnt able to find a description of my exact scenario anywhere.

 

[stem]

Yes, you can extend the thermostat cable if necessary. There are various methods, I usually use a 5A junction box but you could use screw terminals inside an enclosure of some kind. Only the cable sheath should be visible outside of the enclosure or junction box, and the cables secured under cable clamps and / or clipped to a surface.

 

[justbigboned]

Hi Stem,

Just thought you might like to know that I did the installation today and it all worked. Only problem encountered was the dodgy internet on the thermostat, but that was not related to the electricals. Not sure how that will pan out.

Unfortunately I'm going to have to rewire it all properly tomorrow, the original installation (by the builders) was a complete shambles as far as I can see. Rats nest with bonus items. How anyone could be proud of work like that is beyond me!

Had a brown wire that wasnt connected to anything at the wiring center, just hanging loose, and a brown sleeved blue wire from the thermostat below which was missing its sleeve at the wiring centre. I am a complete novice, but that doesnt sound right..!

Thanks for all the help!