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ZC ZR and beyond on TACO SR506 exp for primary pump

Trying to come to grips with a system that we set up primary secondary to limit the problems with low return temps on a Weil McClain Gold hydronic boiler.

There are 4 zones, actually on a SR506 exp but I assume the question is relevant to anything in the SR50x series.

I assumed that once you had the PC70x running through the plug in expansion that I could remove the tab linking ZC and ZR and one would give me 120 when any zone was calling, and the other would give me 120 when there was a fire demand to the boiler. Because you want the primary pump running anytime any one of the secondary pumps is running, even if the boiler is made on temp.

In the old days this all would have been handled between the relay and the boiler, but now with the relay acting as temp reg. for the boiler as well, where do I tap for a primary pump?

My current solution is to go over to a Tekmar 256 downstream of the SR 506 which then just makes it unfortunately redundant that I bought the exp. I should have saved the dough for the downpayment on the 501 I'll need to run the boiler independent of the 256 when the priority circuit calls and I have to jump to the background limits on the boiler to get the temps to make hot water.

Am I missing a contact on the SR506 I could be using, or could I relatively easily tap the circuit board to pick up a demand signal that isn't overridden by the expansion reset controller.




  • SlimpickinsSlimpickins Member Posts: 314

    Not sure why you set up the gold for pri/sec because its already set up that way. There is already a primary pump that circulates within the boiler and a thermostat that opens flow to the heating system at 140 degrees.  Some pics and piping diagrams posted may help.  
  • Primary Pumping Outlet

    If you weren't doing reset, you could wire your primary pump to terminals "Y" and "W" on the boiler.   The SR501 would be the easiest solution.
    Often wrong, never in doubt.
  • kevkev Member Posts: 94
    sr control

    If you take your neutral from the power input terminal and your hot from ZR terminal with jumper in place and power your pump. you can run a primary pump any time zone calls for heat.
  • archibald tuttlearchibald tuttle Member Posts: 484

    don't know. this is a Gold Oil, maybe I should have been clear and there is nowhere in this jacket you could possibly be hiding a circulator that I can see. Might have been a small steamer before I got it relatively newly used and stripped. Maybe they supply the hydronic as you specified.

    But this is a pretty typical 3 section cast iron oil boiler.
  • ChrisChris Member Posts: 3,056
    Page 24

    Page 24 of this should set you straight.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • archibald tuttlearchibald tuttle Member Posts: 484
    edited April 2011
    the problem with that . . .

    . . . is that the ZC/ZR terminals are not hot on zone demand, only on fire call from the PC 700 when the control is in reset mode. The suggestion above and page 24 say the same thing, but it does not work. The circulator only runs when the boiler is firing. Is there something wrong with my control?

    I can't figure what's up with that. those used to be the relay terminals that allowed you to get a signal before and after boiler temp demand as opposed to zone demand.

    I still don't get why you would have the jumper on anyway. I thought the point of ZC/ZR was to give you a choice between being up or down stream of the boiler aquastat, which, in this case is the PC 700. (pg. 24 shows the 702 but same difference).

    I think a friend of mind took some high quality images of the back of the circuit board and we did some tracing once upon a time for something else. I gotta go dig those out.

    Thanks, and if someone can tell me from theory of ops that my control is not working right, or maybe I'm just thinkin wrong.  wouldn't be the first time.

  • ChrisChris Member Posts: 3,056

    What differential setting do you have set in the PC-700?

    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • Gary JansenGary Jansen Member Posts: 56
    Let's check your connections

    1st of all, is it a Weil Mclain WGO-3 water boiler? A Taco SR506-EXP with a PC-700 reset control?  Switches on SR control set to master, reset, and priority off? You don't have a choice of where 120 volts is available in regards to the ZC/ZR terminals. Put jumper back in between ZR and ZC. 120 volts is available at ZR anytime a zone calls for heat. If it isn't you have a bad board. You would only remove the ZC/ZR jumper if you had a boiler with a low limit built into the boiler aquastat. You could add a strap on aquastat in place of a low limit on your boiler, it would then not allow any zone pumps to run until the boiler is warmed up. ZR to strap on common, N/O back to ZC. Boiler pump would need to be wired to boiler aquastat for this to work. But you have the 256 for that mode. One last thought- check your line wiring for proper polarity. If you have it backwards weird things happen. Hope this helps, Gary
  • archibald tuttlearchibald tuttle Member Posts: 484

  • archibald tuttlearchibald tuttle Member Posts: 484

  • archibald tuttlearchibald tuttle Member Posts: 484
    edited April 2011

    [quote]Weil Mclain WGO-3 water boiler?[/quote]

    P -SGO -4  guess I lied about the number of sections. Don't know what the alpha prefixes designate although I'm guessing the S meant it was supplied as a steamer. This goes back a couple years when I got it stripped from a friend who had done a gas conversion for a customer.

    [quote]A Taco SR506-EXP with a PC-700 reset



    [quote]Switches on SR control set to master, reset, and priority off?[/quote]

    Yes, Yes and No, there is an indirect hotwater maker on zone 6 so priority is on.

    [quote]You don't have a choice of where 120 volts is available in regards to

    the ZC/ZR terminals. Put jumper back in between ZR and ZC. 120 volts is

    available at ZR anytime a zone calls for heat. If it isn't you have a

    bad board. You would only remove the ZC/ZR jumper if you had a boiler

    with a low limit built into the boiler aquastat. [/quote]

    ah yes, it all comes back to me now. anti-condensing technology.

    The problem is I don't need a low limited circulator. But just to confirm your point, if I pull the jumper on ZC/ZR and added a close on rise aquastat across those terminals then theory says that no zone circulators would run until that aquastat was made.

    Unfortunately this is opposite of what I'm trying to accomplish because I want a circulator that runs all the time and a boiler that only runs on fire call from the PC 700, but insofar as my tester keeps telling me, and I reconfirmed again this morning, ZC and ZR are NOT HOT on zone demand. Zone circulators are running and there is no juice to ZC/ZR.  So I'm not sure how breaking ZC/ZR would shut off zone circulators, although I believe you are correct about what those terminals were allocated for on the boiler mounted relays where I first got familiar with that coding.

    But worse, from my point of view, Taco shows the system circulator hooked to ZR but ZR is not hot unless there is fire call from PC 700, so this is not particularly useful for primary secondary application with a boiler that actually has some mass in it.

    IT works, I've been running it like this for a couple of years, and using the Ad differential, the control just lets the boiler set point range wider, but I'm leaving hot water in the boiler, might get some ghosting on the primary loop even without the primary circulator, but I think it is likely that without the system circulator running the secondary loop short circulates in reverse direction on the primary.  That is what I think hydraulic physics tells me would happen.

    Of course it is saving me colder starts on the boiler, so maybe I shouldn't worry about, let that heat stay there and radiate into the basement a little bit (where I've never got around to hooking up my floor manifolds), that was one of the first floor pours I did with polybutyl, long before the days of oxygen diffusion barriers and the like although it runs off an indirect so my main concern is back then, late 80s, I got told not to worry about underfloor insulation except on the edges so I'm thinking if I actually hooked it up, I'd be heating a fair amount of the ground and its mostly a storage area. I was going to modestly warm it just to keep the 1st floor floors from being too cold, but I thought better of it for the time being. The manifolds are all made up and just sitting there but . . .

    So, really I'm mostly mystified that I can't get the choice of operating parameters for a system circulator out of the SR506. Hadn't thought of this for a couple of years, but just wired in a fourth zone for my homemade indoor spa that has been waiting for a couple of years - or course got it on line just in time to turn it off for the summer but by god I ran it -- and thought about actually putting the cover on the SR506 (radical thought, I know) and recalled my consternation about this system circulator from a couple years ago. And I had never run the question out here that I can recall, so I got the tester out again and checked the operation of the control and started writing novels on the wall.

    Thanks for your indepth thinking about this,

  • Joe MattielloJoe Mattiello Member Posts: 547
    PC700-2, and PC702

    Hi Brian

    You’re absolutely correct.  Using the SR control and the PC700-2 leaves you with one terminal short for operation of the system pump when piped primary secondary.  However, you do have two options; you can wire the system pump directly for continuous operation.  Some people do this because the boiler is running anyway, and the pc700 controls the boiler temperature. 

    The second option may work better for your application, which includes the PC702 two boiler staging control instead of the PC700.  The advantage is the TT connections are interfaced directly from the PC702, so you can use the ZR terminal on the SR control for the system pump.  This should resolve the system pump issue. 
    Joe Mattiello
    Application Field Service Engineer
    Taco, Inc.
  • archibald tuttlearchibald tuttle Member Posts: 484
    thanks joe

    I like the suggestion on the 702- i happen to have one on the shelf.

    So, to confirm how the interface works, if I use the 702 and tap the boiler off one of the boiler circuits, can I turn off the staging/lead swap functions?"

    And on the SR 50x, I believe you are saying the the 702 will keep ZR  hot with 120(and the x x end switch closed) whenever there is zone demand (denoted as "boiler demand by the 700 and 702 as distinct from the fire call.

    This is a great idea if the above is a correct interpretation of your suggestion and I actually have another 501 I've been trying to trip for nefarious purposes on zone demand and I've been frustrated by the operating scheme.   And  to make matters better, I have a job where I can put my 700 that doesn't require the primary pump function.

    I assume as you look at variable pumps and the future of pumped vs. zoned systems when you update the SR series you might bear this in mind and throw in another relay cube or use zone cubes with an extra isolated contact for the primary pump.


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