Nest thermostat and no C wire at my boiler

Question

so I bought a nest thermostat and it keeps running through the AAA batteries, recommending that I use a C wire, though there's just 2 coming out of the wall (red and white). I got C wire/power adapter to install at the furnace, but there's no clear C terminal, and the wiring/terminals are very different than what I've been seeing in the instructional videos (no W/Y/R/G/C). I'm just hoping to get a little advice on whether this can be done at all, and whether there's a simple solution to connect this C wire (on the adapter) to something or if I'll really just need a pro to handle it.

I've attached a photo of with the connection points circled in yellow.

Answer 1

You "C wire adapter" can probably be used with this system. vYou have "C" available, but not conveniently in a wire or terminal.

1. The two yellow wires that are connected to the thermostat. They are labeled T-T but hopefully one of them is R and one is W. With some thermostats it doesn't matter but for your new one, you need an R. If you know how to use a voltmeter, you want to see 24V between ONE of these and (GND) when the thermostat is not calling for heat. If not, you won't be able to use the new thermostat at all with this system. If yes, it's important that the yellow wire that corresponds to R is connected to the C wire adapter's R terminal, and the other yellow wire to W.

2. The white wire coming from the (GND) terminal on the ignitor is "C". Find the other end of it. Look for somewhere you can connect to easily. Somewhere there is a transformer and that white wire and other things will all be connected to the C side of it. You might need to cut a wire to gain access. Connect your C wire adapter "C" wire there.

Answer 2

I have a house with hydronic heating using a boiler. All of the thermostats have only two conductors run to them.

I have found only two good solutions to this.

The best one is to use a a "common maker" device. I have used multiple of the Fast-Stat Common Maker devices. They work flawlessly.

https://www.fast-stat.com/

If you don't want to do this, there is exactly one wifi thermostat that can operate for 6+ months solely on battery. The Lux Geo https://www.luxproducts.com/geo-4/ I used many of these previously but they're not as nice as using the common maker devices. They are finicky to get into the wifi and have delayed action (I assume to conserve battery)

At your boiler it is easy to add common wires using any number of devices designed for this. In my situation I have five thermostats for the boiler system and I use a Taco ZVC406-4 Zone Valve Control

This will power all thermostats individually and give you a single trigger for the boiler and pump(s).