Wyze thermostat and 24v adapter

[zeb05]

Hello, it’s my first post so apologies in advance if I am not providing enough detail. I have a question about wiring for the wyze thermostat. My current thermostat has two wires, a white wire connected to W and a red wire connected R, there is a jumper between R and RC. There is also a third unused green wire in the wall. The control panel for my furnace is a Honeywell Type L8124A, C L8151A (Triple Aquastat Relay). So the thermostat wires connect to two T/T terminals, and the third unused green wire does not connect to anything. The control panel looks exactly like this: https://support.ecobee.com/hc/article_attachments/360025328511/mceclip0.png

I’ve read several DIYstackexchange articles about soldering the green wire to the second lead of the transformer on the back of the control panel, however accessing the back of the control panel is going to be a massive pain.

Could I buy a 24v AC/DC adapter (Amazon.com) and connect one of the adapter wires to the unused green wire as a C wire? If so, what should I do with the second wire coming from the adapter? Do I need to connect both wires from the adapter to the thermostat? I’ve read that I should connect the adapter wires to C and RC on the thermostat, but I live in Northern New England and do not have a cooling system. So I am hoping I can just plug the adapter in the basement and connect it to the unused green wire then cap off the second adapter wire, instead of having to plug the adapter into an outlet near the thermostat and run cord along the wall.

Any thoughts or advice on this?

[speadie]

You would need both of the C adapter wires to be connected to the wyze, or have the common come from the transformer on your aquastat. Unfortunately, there is no way for the current to make a loop through the load if both transformer wires are not connected to it,

Wyze thermostat simplified block diagrams

I made a couple of simplified block diagrams to show why running the wyze thermostat requires a C wire and why if you use an external transformer, you cannot use the Cooling aspects of the wyze. Not sure if this will help anyone, but it’s worth trying. Current needs to flow through the R and C terminals of the transformer, through a load in order for that load to get powered properly. Without a complete loop back to the transformer, you run the risk of the current finding its way back through…

[dmalloy17]

I am having a similar issue with my two-wire thermostat. My relay is an Aquastat L8148E. I only have hot water baseboard system (no A/C).

I pulled a third wire from my old thermostat to use as my C-wire.

The old thermostat connected just to the T/TV connections for the thermostat on the relay.

Using the new C-wire, I connected the Aquastat to the Wyse Thermostat as shown below…

T------> Rc
W_____> C
TV_____> W1

The thermostat does not power up. I have 24 v between Rc & W1 and between C & W1.

Any suggestions on what I an doing wrong would be appreciated.

[speadie]

looks like you want to hook the wyze up as follows:
Rc> TV
C> W (or Z)
W1>T

[zeb05]

This was both helpful and educational, thank you for the diagram, really appreciate the time you took to explain the answer.

[speadie]

I added an isolation relay diagram to that post, That is what you should be using for an aquastat with T T terminals. If you have 3 wires, then you could hook up an external transformer near your aquastat, send R, C, and W1 wires to the wyze, and connect a 24VAC NO isolation relay across T T with the coil wires being C and W1. This results in a working aquastat, and a working wyze, on only 3 wires.

[dmalloy17]

Thanks for the “speedy” response Speadie. I appreciate your insight and directions.