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Phil, Mechanical Engineer
Category: HVAC
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Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I am trying to connect a new Honeywell RTH6500WF to a Taco

Customer Question

I am trying to connect a new Honeywell RTH6500WF to a Taco ZVC403 Zone Valve Control. This is to replace an old 2-wire thermostat. I have pulled a new 5 conductor thermostat cable, but I can't figure out how to connect the conductors and the boiler side.
The issue is that the thermostat requires continuous current on the C connector in order to operate.
What I tried: R&W to the two T connectors for zone 1. Blue to one of the Transformer connections to the board. Looked good. There were 26v between the R and the B (connected to C on the thermostat).
However when the thermostat called for heat, there was no longer voltage between R and C. There was voltage
to the other side of the transformer, but when the heat call stopped, the voltage switched back to the first side.
I think I need to use a 4th wire, but not sure what to connect to what.
I do have another 24vac transformer I could connect.
Submitted: 10 months ago.
Category: HVAC
Customer: replied 10 months ago.
OK folks. Thanks, ***** ***** figured it out. The weather here is hovering at 9F and there was no way I could go to bed without getting the thermostat connected.
I case you're wondering, I removed the jumper that connected R and Rh at the thermostat. I connected the 2 wires from the "heat circuit" from the zone valve to R and W. I connected the two wires from the transformer to C and Rh. This was not the first combination I tried, but this worked.
Since this question was not answered in a timely manner, and since I answered the question myself, I will deny any charges placed on my account from JustAnswer.com
Thanks.
Expert:  gotoman for ac replied 10 months ago.

Great work man. Sorry I did not get to you. But you did the correct wiring for two wire. Glad you are back online. Bad winter up north right now. Russ

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