Old Gas Furnace with Wall Adapter for C Wire

I’m attempting to install the Wyze thermostat with a fairly old gas furnace. The current Honeywell thermostat has the following wiring:
W - White wire
G - Green wire
Rc - Red wire. Jumpered with R
Y - Empty
C - Empty

There is no Rh spot on the existing thermostat.

I purchased a plug-in 24v wall adapter to supplement since there is no C-Wire. Based on this video - https://youtu.be/gahPxCcPDto - and the Wyze setup I’m using the following connections to the Wyze board:

24v Adapter - into C and Rc (it has two wires)
Red - Rh
Green - G
White - W1

I attempted leaving the red unconnected and that did not work. I’ve tried switching the Red and one of the 24v wires (the Rc and Rh) and no luck either. In its current configuration the Wyze thermostat screen displays ‘Wyze’ but the app says the G wire is missing. Unfortunately, the board in the thermostat was bypassed and the Red/Green/White wires are straight wired into the furnace.

Any thoughts, advice, or references would be appreciated!


You could use an isolation relay on the furnace side to switch the fan separately, or you could just connect the G and W wires together and have the fan always run when the furnace is running. It’s not ideal, but it would work. You should have a fan control if you do this though.

That is very helpful, thank you! Do I need to ‘fake out’ the Wyze app to make it function properly? It really only asks about the existing thermostat configuration (which doesn’t have the C wire). Should I tell the app I have W, G, C, and Rc wires (despite my existing not having a C). Then I’d hook it up accordingly and leave the furnace’s Rc wire not connected?
Thanks again

Tell it you have Rc, C, Rh, and W wires.
Connect the external transformer to Rc and C, the R wire from the furnace to Rh, and the G and W1 wires from the furnace to W1 - You will want a short piece of jumper wire for this, rather than trying to fit 2 wires into the wyze connector.