Wyze Thermostat - 3 Wires (R, W, G) - Not Compatible?

I’ve seen a few other similar posts, but none for my set up and I’m too ignorant of this topic to make sense if there’s a possible work around. I love in an older house that has a very old Honeywell thermostat and only has the R, W, and G wires connected. I have a Rheem furnace and no A/C. We do occasionally turn on just the fan to help circulate the air, but it doesn’t do much. Is anyone aware of any work arounds or changes I can make that would allow me to use the thermostat? Here’s pictures of the connection at the thermostat.

Any help would be appreciated!

Are there other wires wrapped around the thermostat wire, or is this just funky insulation?

Take a picture of the furnace side of your thermostat wire and post it here.

Lol, I thought it was funky insulation too, but when I checked the other end at the furnace it’s easier to tell there are also Yellow, Blue, and Brown wires which are just tightly wrapped around.

At the furnace end. Connect the Blue wire to “C”
At the thermostat, connect Blue to “C”, Red to Rh, and White to “W1”, and Green to “G”
This will supply power on red, blue will be common, White is heat and green is fan.

I’m not familiar with Wyze’s setup, but you should be able to tell it in settings that there is in no A/C installed, or gas heat only


You may have to use Rc instead of Rh, or just jumper between them if it doesn’t power up.

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Blue on both ends to C.
Red to Rc
White to W1
Green to G

Wyze needs Rc to be power source, and if Rh is not present it will just use Rc to switch W1 without needing any jumpers.

UPDATE: It worked! No need for jumpers amd Red to Rc. I forgot to close the door on the furnace, so it automatically cuts the power for safety.

I followed your instructions exactly. There was no power at the thermostat when I used Red to Rc or when I tried Red to Rh. I also tried a jumper between Rc and Rh with Red in Rc. Nothing ever got the thermostat to power up.

A new issue that I’m struggling with is the let red wire at the thermostat is short so I can just barely get it to plug in. Is it safe to splice a piece in so I have some extra length?


Yes you can splice a piece in. Just use common sense (proper size wire nut or butt splice. The wire not seating in the thermostat properly is a common point for power failures. If you have a meter you should be getting 24v a/c between the blue and red

Feel free to add a splice, but be careful when twisting a wire nut onto the thin thermostat wires, they can easily break off, leaving you with even less wire to work with.

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