Taco ZVC404-4 and C Wire with Digital TStat

Majortomm

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"?

Sootmaster

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

EdTheHeaterMan

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

MikefromMn

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

EdTheHeaterMan

MikefromMn said:

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.

Alan (California Radiant) Forbes

If you have no cooling equipment, the jumper can remain or be removed.

fenkel

Have you programed the thermostate correctly?