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End switch failure on ZVC controller - twice

This is the second time in two years that the end switch has failed on a Taco ZVC 404.  The zone valves are opening on a call for heat (yellow and red lights are on), but no closure on the end switch to tell the boiler to come on.

Coincidence or is something else going on?
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


  • Paul S_3
    Paul S_3 Member Posts: 1,257
    edited December 2012
    Taco ZVC 404

    ive had 4 go bad this year already....i use taco and argo.....you are talking about end switch A on the panel to turn boiler on......i would just check out my low voltage connections make sure theres not a loose one...other than that i say its just faulty end switches
    ASM Mechanical Company
    Located in Staten Island NY
    Servicing all 5 boroughs of NYC.
    [email protected]
  • Steve Whitbeck
    Steve Whitbeck Member Posts: 669
    end switch

    Honeywell had quite a bout of that a few years ago.
  • Joe Mattiello
    Joe Mattiello Member Posts: 703
    ZVC control end switch

    I was just reading about the ZVC endswitch failures.  can someone provide the whole model number of the control?  As you may know, Taco has recently introduced the -4 solid state controls. Frankly, the boards have been performing flawlessly.  Appreciate any feed back
    Joe Mattiello
    N. E. Regional Manger, Commercial Products
    Taco Comfort Solutions
  • ZVC

    Sorry, someone else made it to the job before I had the chance.
    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
  • adambuild
    adambuild Member Posts: 413
    Me too!

    First off let me say that I'm a diehard Taco fan and user. I had a service call at the beginning of this season where a zone of radiators wasn't heating. The zone valve was open, both the yellow and red LEDs were lit on the ZVC406 but the boiler wasn't firing. I tested the end switches of the zone valve in question and nothing! I swapped out the head and everything worked?!?! I forgot to call Taco after but would love Joe to take a stab! Curious why if end switch not making that the red LED would be lit? Best of luck, Adam
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,646
    Same thing here

    The red LED is to signify if the ZV end-switch has made, and in turn energizes the coil in the relay which closes the "End Switch" terminals 120Volt side.  In the case I had with the control not turning the Circulator on, I just used the "Isolated End Switch" Common and NO.  If your using 4 wire ZV then the red LED is based on that, for two wire (no end switch in the ZV) then the jumper just makes the red LED come on with the yellow one.  Taco 3 wire is the same as 4 wire as far as the ZVC is concerned.

    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
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