I have a boiler with circulating hot water and no AC, so a fairly simple system. The existing wiring is 3 wire, but the wires as connected are incompatible with Wyze thermostat according the compatibility checker. There are 3 separate zones connecting to the valve. How can I wire this to the Wyze thermostat? Thanks!
This is the wiring at the control panel in the mechanical room with R, C and G wires:
Well, that’s interesting… If I had to guess, I’d say you either have a 3 wire valve or a high voltage valve being controlled on the G wire by that R8239A1052/U Honeywell SPDT fan relay.
So in theory, you could simply connect the White “R” wire to Rc, the Red “C” wire to C, and the Blue “G” wire to W1 on the wyze, and it should work.
The only thing confusing me is the ritetemp, where the Red C terminal from the transformer is on the W terminal. This should result in a short circuit when the heat is on. Of course that A terminal is completely undocumented as far as I can tell, so perhaps there’s something else going on there.
I only see one set of wires going to each thermostat, and one sent of wires going to the relay, so is there a splice somewhere where the colors for the 2 different thermostats change colors?
Example schematic and typical hookup from the manual for the fan relay pictured:
Because none of the terminals other than R, C and G have any wires going to them, I can only assume that the hydronic heating circuit is being operated by that relay instead of a fan motor - I’m assuming a zone valve, but I suppose it could also be a circulator pump.
@speadie, thank you very much for the detailed response! And sorry for the delay in response, I was away from home over the weekend and couldn’t take more pictures. You must have a background in HVAC controls because it seems like you know this stuff inside and out!
I tried to take a picture of each portion of the wiring detail and system to give you a complete picture. Does this change your below assessment at all? Is there risk in damaging the system if I connect it like so, or would the worst case be that it just doesn’t work and I try a different wiring config? Do I need to run power to the Wyze thermostat with something like this, or can I get power off my existing wiring? Or use the Wyze C wire adapter that came with the thermostat?
So in theory, you could simply connect the White “R” wire to Rc, the Red “C” wire to C, and the Blue “G” wire to W1 on the wyze, and it should work.
I agree the wiring on the ritetemp is confusing. Not sure what’s going on there. I also could not find documents on the A terminal.
The only thing confusing me is the ritetemp, where the Red C terminal from the transformer is on the W terminal. This should result in a short circuit when the heat is on. Of course that A terminal is completely undocumented as far as I can tell, so perhaps there’s something else going on there.
Does this picture prove that it is low voltage?
If I had to guess, I’d say you either have a 3 wire valve or a high voltage valve being controlled on the G wire by that R8239A1052/U Honeywell SPDT fan relay.
You’ve got a 3 wire hydronic valve system. In order to use a smart thermostat with a 3 wire hydronic valve, you would need to install a SPDT relay controlled by the R and W wires coming from each of the thermostats so that when they aren’t calling for heat, the valves are closed. The wiring and design of the system would be fairly involved for a homeowner, especially with the cascading valve system you have.
Thanks for the response. What is different about a smart thermostat compared to the right temp thermostat that is existing? What makes the smart thermostat installation more complicated?
The rite temp has that A terminal, which must be acting as a “close valve” signal.
Modern valves are spring loaded and only require an “open” signal, but as far as I know, there are no smart thermostats that have both an open and close signal. This is where the 24V SPDT relay comes in, you can connect its coil to C and W, and have the “close valve” wire attached to the N/C terminal, and the “open valve” wire attached to the N/O terminal. Thus, when the thermostat turns on the heat by connecting the R signal to W, the relay opens the valve, and when the thermostat stops sending power down the W wire (when the heat is satisfied), the relay will go back to its resting state and send power to the N/C wire to close the valve. Without that relay, the heat would never shut off. Modern thermostats don’t have a “close valve” terminal.
here’s a simplified block diagram. Your system has the valve end switches (not shown on this diagram) all daisy chained to each other to cause the main boiler to turn on if any zone is calling and off if none are calling.
Wow, thanks for such a detailed response and diagram! I think I understand the overall wiring with the relay you’re describing to accommodate for the valves that are not spring-loaded normally closed. The valves are interesting, the visible notched disk to manually operate the valve only spins clockwise, and to close it, start spinning the disk and the motor will take over and turn more clockwise to close the valve. To confirm, I’ll need 1 relay for all 3 valves, splicing into the existing C wire from the relay to the first valve? Is the C wire then daisy chained to all 3 valves? I then need to figure out where to land the open and close wire from the thermostat on the valve.
You’d need a relay for each smart thermostat. The wire currently coming from W on each thermostat should be the “open” valve wire, and the wire coming from A, or the cool contacts on the mercury switch thermostat should be the close valve wire. The daisy chaining that is already connected should be able to be left alone, as long as you hook the relay up correctly. With the additional load from the wyze and the relay, you may end up needing a separate transformer to run the wyze and relay. If that’s the case, you can connect it like this:
Take lots of pictures and label everything before you take any wires off if you plan on doing this yourself.
