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  1. #1

    Taco ZVC404-EXP Problems

    My 8 Zone radiant floor heating system is controlled by 2 Taco ZVC404-EXP Controllers. One is the Master and the other one is the Slave. The system is 3 1/2 years old and has been working fine up until last week. I noticed that some of the zones were not heating properly. After further inspection here is what I found:

    Master: Zone 1 is not working properly. When Zone 1 calls for heat, the boiler starts, the zone valve opens, but the circulating pump does not run. When zone 2, 3 or 4 call for heat, the boiler starts, the zone valve opens and the circulating pump starts running (they are working properly).

    Slave: Zones 2, 3 & 4 are not working properly. When Zone 2, 3 or 4 calls for heat, the boiler starts, the zone valve opens, but the circulating pump does not run. Zone 1 is working properly. When zone 1 calls for heat, the boiler starts, the zone valve open and the circulating pump starts running.

    Are both controllers bad and need to be replaced? Thanks for your help.

    Mark

  2. #2
    I checked the Zone Valves. Placing a jumper wire between terminals 3 & 4 on the control panel started the circulating pump. I also checked the voltage between terminals 3 & 4 and it was +/- 12 volts. The voltage between terminals 1 & 2 is +/- 25 volts. So it appears that the Valve Actuators on the zone valves must be bad.

    The Zone Valves in my system are Caleffi Z-one Z111000. Is it common to have 4 out of 8 Zone Valves fail at one time? Is my analysis correct?

    Thanks,
    Mark

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