I was having similar problems. I have an older home with a multi zone radiant heat. I bought a Wyze thermostat as a test to replace an existing battery powered thermostat. Upon initial install I found my thermostat wire only had two wires and would not power up my thermostat. My multi zone controller (Erie VL500) had 24 VAC available to power the thermostat, but I was still one wire short to give the thermostat the common it needed. Only having two wires I felt I had five choices:
Run new cable. (Old house and who’s got time for that!?!?)
Do nothing and keep the existing thermostats. (BORING!!)
Run 24 VAC to thermostat from nearby source. (Again, who’s got time for that?!?!)
Find a 3rd party solution that meets my criteria.
Sell the house and buy a home that has more than two wires in the thermostat cable. (Seems a bit aggressive!)
FYI - I chose solution 4. I used the Fast-Stat Common Maker product and it worked awesome! I have just purchased 3 more Wyze thermostats and Fast-Stat Common Makers for my remaining zones.
I had two wire thermostat as well. I tried to use the Wyze supplied C-wire adapter but it didn’t work and was doing all sorts of funky things to my furnace. The 24V doorbell transformer did the trick!! Simple enough for me. Rh and W to thermostat, Rc and C to 24V transformer. Done.