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.

Millivolt aquastat L8148J with Taco sr503-exp-4

How do I/can I use a Taco sr503-exp-4 with an L8148j aquastat? Can I wire XX to TT TV on the aquastat? I want to control a primary pump and two additional circulators on the secondary piping.


  • Ironman
    Ironman Member Posts: 6,863
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • HydroNiCK
    HydroNiCK Member Posts: 123
    Can I leave the primary circulator on aquastat's c c and have it energized whenever a sr503 turns on if I didn't use sr503 primary pump ON setting. In other words primary circulator wired to aquastat in parallel to secondary circulator wired to the taco switching relay?
    HVACNUT Member Posts: 4,560
    Yes. XX on the SR504 to TT on the aquastat. Any zone that energizes on the 503 will close XX, initiating a call to the aquastat and powering B1 and C1.
    My setup is similar, but not millivolt.