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Taco ZVC403 not turning on boiler pump on one zone

Hi, any help would be great...this system worked well for me the last 10 years but Zone 1 is now not working. Zone 1 has both a timer and a sensor to turn on the pump. Last year it became intermittent, this year inoperative for both the timer and sensor. Zone 2 and 3 are on timers and both work fine. The Taco green light is on, and the zone 1 red light and yellow light are illuminated but pump is not on. I do notice in this case that the red light is somewhat fainter and flickers a bit. Could that mean the zone 1 valve could be stuck midway and there is not enough flow to trigger the boiler pump?When I turn on zone 2 or 3 fluid is passed through zone 1 as well and the zone 1 red light lights up bright, so the zone 1 valve I believe is open. Any ideas?


  • STEVEusaPA
    STEVEusaPA Member Posts: 6,505
    edited December 2019
    What kind of 'timer' and 'sensor' are you talking about? And how do they fit (wiring/operation) into the picture.
    Do you have any pictures?

    There was an error rendering this rich post.

  • williamrbecker
    williamrbecker Member Posts: 2
    Thanks! The timer is an Intermatic spring wound interval timer (you twist it to turn it on for the number of hours you want). The sensor is a Tekmar Ice Sensor 090 that is part of an automatic snow melt system, Tekmar Show Detector and Melting Control 665. Both the timer and the snowmelt system charge or cross two wires to activate the boiler and pump. These two wires meet at the same point at the Taco ZVC403 zone 1 connector.
  • GW
    GW Member Posts: 4,703
    Try disconnecting the the zone valve wires And thermostat wires for that particular zone. then jump your r w. Does the light now look normal?
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,646
    Is there an end switch on this, or are #3 and #4 jumped?
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!