On Saturday, December 14, 2013 at 7:52:40 AM UTC-8, Ian wrote:
I am installing a new NEST thermostat, replacing an old two wire mercury bulb furnace thermostat. There are only two unmarked wires. There's 24 V across the wires.

Can anyone tell me which letters on the NEST base (W, Y, O/B, AUX, E, G, C, etc) they will map to? It has to be the most basic of installations; open or close the circuit.

Thanks,

Ian

I am considering buying a NEST thermostat today. I have one of the basic two wire thermostats where I have a white and a red wire. It's the type with the mercury bulb.

The guy came around from the installers and tried installing a nest three months ago and told me it would not work on a two wire system. I have heard different stories about this. Some say yes it does work, other say it won't work without pulling through a common wire (whatever that is, I am no electrician) My two wires are red and white BUT I also have two other wires that are there, a black and a green one that weren't connected at the thermostat. I am wondering if I could use one of those wires as a common if need be. I would imagine they are for a future install of a heat pump.

Can anyone advise me on this?.

Thank you.

On Saturday, December 14, 2013 at 7:52:40 AM UTC-8, Ian wrote:
I am installing a new NEST thermostat, replacing an old two wire mercury bulb furnace thermostat. There are only two unmarked wires. There's 24 V across the wires.

Can anyone tell me which letters on the NEST base (W, Y, O/B, AUX, E, G, C, etc) they will map to? It has to be the most basic of installations; open or close the circuit.

Thanks,

Ian