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Taco ZVC404-4 and C Wire with Digital TStat

I have a Taco ZVC404-4 that was installed last year connected to my boiler for heat in 3 zones. Zone 1 upstairs heat, Zone 2 downstairs heat and Zone 4 (priority) for sidearm hot water heater. 

The current Tstats are wired R & W only with the C on the Taco not used.  I recently purchased a smart thermostat (Wyze) to test out and I have connected it to my upstairs Zone 1. 

The Blue and Green wires running to the Tstats are not connected so I connected the Blue to the C on the Taco controller for Zone 1.  I then wired everything to the thermostat as instructed: R to Rh, W to W1, and C to C. When I connect the smart thermostat it doesn't power up at all.  When I connect the old honeywell Tstat everything works (battery powered) and triggers the zone controls as expected. 

Am I missing something? Is there anything I need to do on the Taco board to enable the C? What are some troubleshooting steps I should be trying to eliminate any possible issues before I declared the new smart Tstat "dead on arrival"?

Comments

  • Sootmaster
    Sootmaster Member Posts: 14
    Are you getting 24 volts between the C&R wires at the thermostat sub-base? Maybe your C has a break between the boiler room and the thermostat. If no voltage- try it right at the zvc control. Cheap meter from the home center is all ya need
    HVACNUT
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,713
    Try using the Green wire for common. Also be sure the TACO 404-4 thermostat wire is connected properly. On a 2 wire thermostat setup, you can reverse the R and the W at the thermostat or the control without any problem. When you use a common... You must wire R on the control the Rh on the thermostat. So look inside the Taco Control and the thermostat to see that the wires are not crossed.

    Taco Thermostat
    ..R.............Rh
    .W.............W
    ..C...............C


    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
    Zman
  • MikefromMn
    MikefromMn Member Posts: 9
    Do you need to jumper the R & Rh terminals in the thermostat?
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,713

    Do you need to jumper the R & Rh terminals in the thermostat?

    That depends on the inner workings of the thermostat. Some must have power to R or Rc for the thermostat microprocessor to operate. Then the answer would be YES .

    I'm not familiar with Wyze thermostats. The original post does not indicate that to be the case. You do bring up a good point though. Something to look at if the system fails to operate with Rh only.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • If you have no cooling equipment, the jumper can remain or be removed.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • fenkel
    fenkel Member Posts: 162
    Have you programed the thermostate correctly?