Installation 2 wire to Y-C-W-G-R-OB

[Ed33]

Hello,

We have an old Honeywell thermostat - that uses 2 wires - W and Rh. The new Nest thermostat that I purchased has 6 connectors Y-C-W-G-R-OB (unlike most video online that has 😎 - could not find anything that tells me how to connect these two wires to which of these 6?

We have heat only system.

Appreciate if someone could guide me.
Thanks

[dmanc53]

I just installed the same.  w is heat and r is power.  green is connected but no blower needed.   

Mine works connecting to the w an r on the nest.  my question is how does it stay powered???? c wire is not used/  I'm afraid to go away and have my pipes freeze if this stops!  does it draw power from the red wire?

[Markjosephp]

Hello folks,

Thanks for reaching out! It sounds like you both have a heat-only system with an old Honeywell thermostat using two wires (W and Rh), and you're looking to connect them to a new Nest Thermostat with six connectors (Y, C, W, G, R, OB). In a heat-only system, you won't use the cooling-related connectors (Y, C, G, and OB).

Here's a simplified guide to connecting your wires:

• Rh (old thermostat) to R (nest): This is your power wire. Connect the Rh from your old thermostat to the R on your Nest Thermostat.
• W (old thermostat) to W (nest): This is your heating wire. Connect the W from your old thermostat to the W on your Nest Thermostat.

Since you have a heat-only system, you won't need the other connectors like Y (cooling), G (fan), or OB (reversing valve for heat pumps). C (common) is typically used for systems that require a power source, and it might be necessary for your setup to deliver constant power to the thermostat and avoid power issues.

Let us know if you have more questions in mind.

Regards,
Mark

[dmanc53]

on the nest, learning thermometer, if there’s no C wire, how long does the battery power last? is it getting power from the W and red wires? What if there isn’t a Wi-Fi connection/interruption. I worry about this failing while I’m away.

[dmanc53]

Will I get a notification if the battery is low?

[Ed33]

Thanks Mark for detailed information - was able to replace the thermostat and the furnace did turn on. However it looks like the power is not sufficient to run Nest - got the C wire from Google - unfortunately, I have a very old (60s) gas furnace that does not have any marking to help me understand how to wire the C-wire I received (does not look like I can share a picture here). 

As its running on battery only - most of the function do not work - likely to conserve the battery. 

[dmanc53]

so has anyone had the experience of the nest learning thermometer, draining power, if it’s relying on battery only?

[Markjosephp]

Hey there,

@Ed33, glad to hear you successfully replaced the thermostat and got the furnace working. Dealing with an older gas furnace can be a challenge. Regarding the C wire, since your furnace is from the '60s and lacks markings, it might require some manual tracing of wires to identify the C terminal. You could try checking the furnace's documentation or reaching out to the manufacturer for guidance.

@dmanc53, if your Nest Learning Thermostat doesn't have a C wire, it relies on its internal battery for power. The duration the battery lasts can vary based on factors like system usage and the frequency of adjustments. The thermostat can draw power from the W (heat) and red wires, but this may not be sufficient for long-term use.

If the battery is running low, Nest Thermostats are designed to send a notification to your connected devices, giving you a heads-up before any potential failure. While some users have reported issues with battery drain, it's advisable to ensure a stable Wi-Fi connection to prevent any interruptions, especially if you're away for an extended period.

Warm regards,

Mark