Thermostat with external transformer

It’s great it comes with C-wire adapter but I needed a transformer. Easy enough to connect the transformer to the outlet, one wire to C the other to RC.
Mine was $20 on Amazon


I’ve had to get one as well, but hasn’t came in yet. I have a radiant floor heat system that just has two wires running from the thermostat to the switch that turns on the water pumps.

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Sounds like my project. I am interfacing the Wyze Thermostat with an old millivolt heating system. Ordered the extra parts I needed off of Amazon. My transformer arrived yesterday but the relay I also need isn’t here yet.

I was able to successfully power up and configure the thermostat with the transformer connected as you noted, to Rc and C. I then will be using a 24vac relay with its coil connected across W and C. The normally open contacts on the relay will then close the circuit to my millivolt heating system when heat is called for.

While I won’t get as much advantage with the Wyze Thermostat as others with more sophisticated HVAC systems will, I am looking forward to monitoring and managing the home heating remotely. :slight_smile:

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My relay arrived today and I now have my Wyze thermostat running on an external transformer and controlling my old millivolt heating system. :slight_smile:

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I have radiant heat as well. I ordered my transformers the day I ordered the thermostat. Installed the first one on Sunday. Working great.

I will note that the app kept saying I had too many wires hooked up or not enough.

The transformer is hooked to RC and C. The wires for the pumps are hooked to RH and W. It is -20 right now so I am glad it is working right.


I can confirm that the Wyze thermostat works with 2-wire heat-only millivolt systems without the use of a relay. All it needs is a 24VAC power source connected to C and Rc to power the thermostat itself. It then provides the needed closure between Rh and W that activates the millivolt gas valve using the small DC voltage (250-750 millivolts) that’s continuously generated by the thermopile using the heat of the pilot flame. (Having read others’ experiences, I’d bought a 24VAC SPST NO relay, but didn’t need it.) With the Wyze thermostat connected as above and the pilot lit, selecting those four connections in the setup app satisfied the app’s connectivity test, allowing normal setup to proceed. My propane wall furnace (no blower) has been running in this configuration for about 20 hours so far.

  1. 24VAC connected to C and Rc
  2. Two thermostat wires connected to Rh and W

Including this possibility in compatibility specs would allow a substantial number of potential customers in climates such as coastal California, where these simple heaters are common, to benefit from the Wyze thermostat.

The one advantage of the old 2-wire thermostat was that it requires no external power, so I’d have heat in electrical outages without needing to arrange standby power to the thermostat. I got around this by leaving it connected in parallel with the Wyze thermostat. It’s set to a minimum temperature, so will have no effect unless I need it to.

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Mine did the same thing twice. There should be a skip option show up.

I wired it up just like the instructions pictured.


Mine did that.
I unplugged the wires from the Thermostat to be sure they weren’t touching inside the wire block.
Re-ran the check and it worked.

I just received my thermostat - should I also get a transformer? I do not have in floor heating. I am confused on this thread as to why you needed one. :slight_smile:

My battery-powered Honeywell thermostat runs on three wires to a Trane gas furnace. Do you think this same power adaptor solution that you got to work on a two-wire system would work for me? Any way to make this work with a battery (since I don’t have a power outlet near my thermostat)?

Am I right to assume I plug the new 24VAC in to C and Rc. Then I take my existing thermostat wires (currently going to W and R and those will go to Rc and W1?

Meaning Rc has two wires on it?

Can you include a link to the transformer that you are using or a pic?

Your 24VAC external transformer goes to Rc and C, your thermostat wires for your heat go to Rh and W1.
Tell the wyze that you have those 4 wires and it will switch its internal configuration to match your wiring.


Hi somebody can help me to install my thermostat? I’m really confused because I don’t have the C wire, and when open the A/C for the motherboard, I couldn’t find it, so im thinking that maybe can use a external transformer, but the old thermostat has already the cable in Rc. . Pic attached

Check behind the old thermostat in the wall for other thermostat wires. If you don’t have any, you will need to open up the air handler and use the C adapter. Show a picture of your A/C or your air handler (wherever the other ends of those wires are) and I can help you find the C wire and make a diagram for you to help you know how to hook up the C adapter.

Hello There.

Need help. I got the 24V transformer as the C wire adaptor didn’t work out well for me.

Here is a pic of my original config on the left. I then connected the transformer to C and RC as seen on the right.

Ignore that the G is dangling. I initially had it all connected. The Wyze app won’t let me proceed and flags an Extra wire in the config check. How do i hook this up properly or in the app?

thanks in advance!

You shouldn’t need a c transformer or a c adapter, as you have a blue wire that you could use for C

Thank you for spotting that. I tried it again and all I get is a clicking noise. Thermostat just keeps clicking using this config. The wyze logo doesn’t come on the monitor, but the clicking can be heard. Any other suggestions?

And for reference here is the pic of the circuit board in the AC (attic)