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.

Need help with boiler and Taco ZVC403-4 (I added second zone to system)

Hello Folks
I have an older home with boiler and cast iron radiators and cast iron baseboards. I added a second zone of copper finned baseboard to the upstairs- as there was no heating on the second floor. I have added a second pump and zone valves to the old and new zones. I have a Taco ZVC403-4 controller that I was told should be all that I need (and I believe that may be incorrect). Can I control and drive the 2 zone valves and 2 motors independently as heat is requested from one or both of the zones? Looking at the wiring diagram for the circulator pumps, there is one connection for a system pump (which runs whenever ANY zone valve opens.) And connections for a secondary pump to either a NO or NC terminal. What I need is for either zone pump to be able to run as heat is needed independently. Any help would be greatly appreciated. I think I may need additional or different equipment.

As a final ditch effort I called Taco support and they say I need to add a SR501 or SR502 depending on who I talked to there....... ? I’m totally confused now. And if so how do I wire them together?


  • kcopp
    kcopp Member Posts: 4,392
    You use either 2 zone valves and 1 circulator OR 2 circulators...
    Sr 502 if you use the circulators.
    ZVC 403 for the zone valves. The boiler will control the circulator then.
    What do you have for a boiler.
  • stonewallpug
    stonewallpug Member Posts: 2
    I have an old Burnhan boiler. P-205ah-wnt

  • SuperTech
    SuperTech Member Posts: 2,120
    It looks like you only have one circulator on the return, next to the boiler. Unless there's something that isn't shown in the picture. Can you please post some pics of the zone valves and near boiler piping? It's usually either one circulator and zone valves or multiple circulators. A system can have both, but it's not common.