Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Taco zvc404 no Zone lights at all

all zones have hot water running through them when only 1 thermostat is calling for heat...any ideas what's wrong?


  • kcopp
    kcopp Member Posts: 4,256
    tell us more about the system... brand of zone valves? Is it possible the valves are left in the manual open position?
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,236
    Something wrong.
  • cobracop44
    cobracop44 Member Posts: 2
    Honeywell valves , they are not in manual mode, I used to have red yellow lights on the panel now only 1 power light,  there is no power to any zone valves when any of thermostats call for heat
  • Jamie Hall
    Jamie Hall Member Posts: 21,517
    Presumably zone valves? First thing I'd look for would be miswiring. If all the zone valves are open, something is miswired. Could also be ghost flow, although that is usually much less flow in the "off" zones than in the calling zone.

    On the other hand, if the Taco never shows a zone valve calling, but the zone valves are open, it is definitely miswiring.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    HVACNUT Member Posts: 5,247
    If one zone is calling, why isn't that light lit? 
    If there's heat on all zones, then either all valves are manually open, all valves are being powered open, or a combination of the two.
    Nobody did any wiring between last winter and now?
    Do you have an electric meter?
  • neilc
    neilc Member Posts: 2,221
    new batteries in the thermostats ?
    known to beat dead horses
  • SteveSan
    SteveSan Member Posts: 184
    Do you have voltage between 1-2 either on a call or no call at the zone valve terminals on the Taco control? Try removing the t-stat wires to the R-W and jump RW to see if it creates a call. If all else fails please give us a call tomorrow 401-942-8000 and just ask for Tech Support. We are here 8am-5pm EST. Please be in front of the control when you call.
  • Joe Mattiello
    Joe Mattiello Member Posts: 667
    Taco zone valve with diagnostic lights are awesome; are your valves two wire? At the bottom of the control there are terminals 1,2,3,4. 1, and 2 are 24V power to valve, and terminals 3, and 4 are receiving signal from zone valve that there's a demand from thermostat, valve opened and fires the boiler. You can place a jumper across 3, and 4 to simulate an end switch closure to illuminate the light, and close the main end switch to fire the boiler. The instruction sheet shows a jumper in one of the schematics. For additional information, you can contact taco tech support at 401-942-8000 and ask for tech support.
    Joe Mattiello
    N. E. Regional Manger, Commercial Products
    Taco Comfort Solutions