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Taco SR502 with SR501 for circulator?

lewkew Member Posts: 6
edited January 2018 in THE MAIN WALL
What I have:
- Gas fired steam boiler provides single-pipe steam heat to old part of house (steam thermostat directly wired to boiler).
- SR502 controls hot water loop for home addition ("zone 1") and Buderus indirect [potable] hot water ("zone 2 priority"). When either zone is triggered water is circulated from an indirect [non-potable] tank (see SR501, next).
- SR501 circulates hot water from boiler to indirect [non-potable] tank, with pump. Aquastat on boiler is 180 degrees, aquastat on tank is 160 (the pump switches on when tank temp falls below 160, moving water from boiler; the boiler is fired when the water coming out of the boiler falls under 180 degrees... yes, I know there's a differential so the numbers are a little different but you get the drift).

ISSUE: The SR501 turns "on" whenever the temperature in the indirect [non-potable] tank falls below 160 (aquastat has 5degree diff so really 155). This is money-wasting during all the months of the year when the heat isn't needed (Buderus only needs heat after showers/baths/etc; this dumb SR501 fires all day and night because this is in an unconditioned basement).

What I'd like:
- SR501 should only turn "on" when the SR502's zone 1 or zone 2 are on. In other words, SR501 should be conditionally powered. I think this should be straightforward: draw power from the ZC/ZR on the SR502 to the N/H on the SR501. ...but before I burn my house down has anyone else out there tried this? Other approaches? I'm happy to pay an electrician to do it, right, but seeing as I paid one to do it wrong (ie, what I have now) I'd like to know the correct answer before I shell out more $$$. Thanks!


  • STEVEusaPA
    STEVEusaPA Member Posts: 6,132
    How do you plan to get domestic hot water in the summer, wired the way you suggest?
  • lewkew
    lewkew Member Posts: 6
    When the Buderus calls for heat (zone 2 priority on the SR502) it will turn on. This will power on the SR501, which (now on) will register that it needs to turn on the boiler to heat up. It will do so. The total time to heat the buderus (domestic water) will take longer in the summer, but my domestic hot water needs aren't sufficient to feel this pain. Of course, I am open to alternative suggestions that don't involve an indirect tank burning natural gas to heat itself for no good reason... daisy-chaining the 501 to the 502 is the best I can think up, that's all.
  • info43
    info43 Member Posts: 51
    I booked marked this link for myself a while ago. It might have what you are looking for.

  • GW
    GW Member Posts: 4,605
    That will work, you’re wait time will increase some of course. I don’t follow your idea though. Why not take your end switch from the 502 and send the signal to the TT of the 501? I may be missing something. You’ll want a strap on Aquastat to keep the boiler from steaming, right?
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    [email protected]
  • lewkew
    lewkew Member Posts: 6
    Thanks, Info43 and GW! Very helpful to read the other thread, to see what other people have tried. GW, you're exactly right (that's much smarter and simpler than my idea). And yes, *very* good advice on the boiler aquastat.