Wyze Thermostat Compatibility with Heat and Cool

Hi, all. I first tried reading through all of the thermostat compatibility threads to see if I can find a solution to my problem, but it seems each are unique. Sorry for posting yet another thread on this topic, but I’m not sure how else to get help.

Just got my long-awaited Wyze Thermostat yesterday, Excitedly began to install when the app on my iPhone immediately deflated my excitement when it told me my system is not compatible. I only have 3 wires behind my current thermostat: Y, W, RH. My carrier furnace and AC is about 10 years old. The wire from the thermostat leads to the basement and is spliced with a 5-wire line that goes to the furnace. So it seems that my furnace can take the 5-wires, but my thermostat is using only 3 of the wires. I am attaching photos of the wires behind the thermostat, the spliced connection between the thermostat and furnace: 3-wires from the thermostat and 5-wires to the furnace, and the description panel showing the model #, etc, of the furnace. I am willing to run new wires if necessary, but just want to make sure that my equipment, as is, will have full compatibility with Wyze Thermostat if I spend the money and time to do so. Pleas help! I really don’t want to return this thermostat! Thanks!

I think you need a C wire and that is why it is telling you it’s not compatible. In your case, the operation of the thermostat should be very simple - call for heat, call for cool, or do nothing. Maybe look into using the adapter.

Thanks, obxer. I do have the adapter that came with the Wyze thermostat and am very willing to use it if it’ll make my unit compatible. I would have assumed that the app would have given instructions to install the adapter in my case. I just stopped when it told me it’s not compatible. If I install the adapter, will I still need to run new wiring? Sorry, I’m not very electrically savvy.

I’m not really familiar with this situation as it didn’t apply to me - and I’m certainly not expert. But my understanding is the C wire is required to power the thermostat. I’d try using the compatibility checker but include a C wire. If that says your unit is compatible, then use the adapter or figure out how to get a C wire run. Maybe there’s an unused wire tucked back in the wall behind the thermostat that will help.

Do you have more wires in the wall behind your thermostat? Also, do you have a picture of your furnace board?

If you don’t have more wires in the wall, you would need to fish new wires from your thermostat down to that junction point.

Thanks, speadie. There are only 3 wires behind the thermostat, but it is connected to a 5-wire set in the basement leading to the furnace. Here is a photo of the wire configuration on the furnace board - there are 5-wires. I’m thinking that I should be able to just extend the 5-wire cable up to the thermostat?

The com wire hooked up at your furnace probably feeds the AC unit outdoors, Do you have more wires in that hole? preferably a blue wire, as that is the traditional color for the C wire leading to a thermostat. And yes, if you need to run both a heat and cooling system, you will need at least 4 wires.

Ideally, the colors to the thermostat would be

Are you able the see the photo attached to my original post? There are only 3 wires to the thermostat: red, white, and blue. But the blue one is hooked up to Y at the thermostat. Again, however, this 3-wire cable from the thermostat connects to a 5-wire cable leading to the furnace.

Yes, I see it. I also see that your 3 wire run has spliced the yellow wire with a blue wire. Just saying that when you run new wires from the thermostat to that splice, you should fix the color coding of the splices. that way the colors in your furnace will match the colors in your thermostat.

You’re going to have to run a new cable from the thermostat, no way around that, but you only need to run it down to the splice. You can just see the blue wire that should be connected to C on both ends in the hole that the wires come out of on the furnace.


Got it! I have yet to get new wires, which I will do soon. I’ve never fished wires through a wall, but I’m hoping the old wires to the thermostat is easy to pull out. Any ideas on how to tightly secure the new wires to the old so that it doesn’t disconnect inside the wall? Finally, where would the blue wire connect to the furnace board? I don’t see a “C”, or is that the same as “Com”? And where would I connect the W, Y, R wires on the Wyze thermostat panel plate? Thanks?

Here’s an updated schematic… Thanks for pointing out the blue wire hidden in the hole in the furnace. I opened it up and found it! Where would I connect this blue wire on the furnace board?

C is the same as Com. Speadie did a GREAT job of investigating and analyzing your problem and providing all the info you need for the solution. Just follow his advice and maybe search for “Basic Thermostat Wiring” using Google for some basic info on wiring thermostats - there is plenty that is easily available.

Then use the instructions in the app when you do the setup. Start working and let us know how it goes for you. If you’re still having difficulty you might want to call a professional to make sure it’s done safely and successfully.

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Thanks obxer! Final question: I don’t have a green (G) wire connected either on the furnace board nor the thermostat, which is supposed to be for the blower. I assume this is okay because because my blower has been kicking on without the G wire. The Wyze app set up guide will not let me get through unless I select that I have either G or C wire attached, which I have neither of at the moment. Am I correct in assuming that as long as I run a C wire up to the thermostat, then connect the C wire to “Com” on my furnace board, I should be good to go? Also, another wire is already connected to “Com” on the furnace board - which I assume leads to the outdoor AC unit. Is it okay to piggy-back the blue C wire onto this same screw/port leading to the thermostat? In other words, there will be two wires in “Com” on the furnace board, per the attached diagram shows - one to the AC, and one to the thermostat. Basically, should I follow exactly the wiring on the attached diagram, except for I won’t have green? Again, thank you VERY MUCH for the help!Furnace-Thermostat-Wiring-and-Troubleshooting-Diagram

Yes, should work fine. As speadie said, you need the C wire. And seems the G wire is not needed in your case - your furnace and AC must be controlling it automatically. I’d try it without it and make sure it works as it did. Maybe try adding it later if you want to be able to switch the fan on by itself manually. And many of us are having problems - so keep your old t’stat around in case you can’t get things to work right and want to put it back in for a while,

UPDATE: Thanks, speadie and obxer! I ended up fishing a new thermostat wire through the wall and connected it at the junction. I utilized all 5 wires! There was a green a blue wire at the furnace board, so I ended up hooking those up, too. Whereas I didn’t have a G wire before, now I do! I completed the setup on the app, and viola!!! It works!!! Thanks again for your help! Happy 2021!!!

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I’m also trying to replace a Honeywell to a Wyze thermostat. My heat runs on gas and AC is electric. Attached are my current connected wires. Please help.

You have a wireless thermostat. Unless you have more than 2 wires going to your thermostat, you will be unable to use the wyze.

First of all, thank you. Second, I’ve been reading on some forums about a transformer to power the thermostat separately. It seems from your answer that it would not solve my problem. Is my thermostat currently power by wires and wirelessly commands my unit? Am I understanding this correctly? Thanks!!