Nest install advice

[Andy_Cov]

Hi,

I'm currently contemplating replacement of my room thermostat with a Nest thermostat, but I have a quick question about installation.

I currently have an Ideal Icos HE12 boiler, with a Drayton 522 timer. The room stat is a Drayton RTS1, and is mounted about 15m from the boiler. There are two zone valves on the boiler - heating and hot water. All wiring was buried by the housebuilder during the original installation, and I don't have the option of easily changing / modifying this wiring.

I've checked the wiring at the thermostat end, and I have 4 wires - live, neutral, call for heat and earth. There are no other wires available within the cable running to this point.

Having checked the installation guide for the Nest thermostat it makes reference to a common wire, which I don't have.

My question is - is this needed? I seem to see conflicting reports elsewhere.

 

[Cgas]

Never fitted a nest or seen one fitted so can't really give you a 100% answer but use the live as your common and other wire for the switch? Plus your usual neutral & earth ?

 

[Dan Robinson]

edit... looking at the wrong manual.

 

[Andy_Cov]

Never fitted a nest or seen one fitted so can't really give you a 100% answer but use the live as your common and other wire for the switch? Plus your usual neutral & earth ?

Normally, I'd do this, but the Nest has five connections - live, neutral, call for heat, common and earth. Reading around, it seems that common is a low-voltage live. I don't have this, but can't help wondering if this only applies where the switching circuit doesn't run at mains voltage. Do I just bridge common to live?

 

[Dan Robinson]

Earth? In the Nest?
Call a professional.

 

[Andy_Cov]

Earth? In the Nest?
Call a professional.

Misremembered the earth - there isn't one. It's just the common that I have a question on.

 

[muggles]

Link the Common across from the permanent live inside the Heat Link

 

[Andy_Cov]

Link the Common across from the permanent live inside the Heat Link

Thanks - just what I was looking for.

Did a bit more investigation on my system earlier and discovered the wiring centre behind the hot water cylinder on the top floor. Not so good was the moment when I opened it up and discovered that the internals had never been fitted and it was effectively a box with a couple of unlabelled connector blocks in it, which bear no resemblance whatsoever to the legend inside the lid.

To add to the confusion, I know that I'm looking for a grey wire, a black wire and a red wire that run to the room thermostat point. From the wiring centre, there are four grey wires, three black wires and two red wires that run in the direction of the lower floors. Oh well, looks like I've got some detective work with a multimeter to do...