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  • Boiler aquastat wiring question

    I have what I think is a simple question, which I hope maybe has a simple answer ...

    My oil burner has three zones: two heating zones (1st and 2nd floor) and one Amtrol tank. The aquastat is a Honeywell L8124 (a/c), and this is connected to a Taco SR three zone switch. The Amtrol is wired to the first zone in the SR503, and is supposed to be in priority mode. First floor is on the second zone, second floor on the third zone.

    Here's the issue: I've just noticed that when the Amtrol on zone1 calls for heat and the furnace starts, my first floor circulator also starts to run. This causes the first floor to be warmer than it needs to be, and the boiler to run more often than it should.

    I've checked that when the second floor calls for heat, the first floor doesn't run, as it shouldn't.

    As far as I can tell from the wiring, the thermostats and circulator inputs are wired correctly. ZR/ZC from the aquastat are wired to ZR/ZC in the SR503. There is a jumper in the 503 between ZC and X1. Everything looks so straightforward. And yet ...

    Does anyone have any ideas?

    Thanks!!

  • #2
    Re: Boiler aquastat wiring question

    Neither ZC or ZR should be used with the SR relay. The end switch in the SR control should call TT on the L8124. And you should either bypass the low limit on the 8124 or swap it out for an L8148 that does not have low limit control.

    Unless you are running a primary circulator you should have nothing wired to C1/C2 on the 8124 either. All circulators should be wired off the Taco controller.
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    • #3
      Re: Boiler aquastat wiring question

      Thanks very much for the reply ... hope you don't mind if I pick your brain a little more!

      1) From what you said, I see what they did. It's currently wired in what the SR503 says is "tankless boiler application" mode. So, to confirm, what I want is "cold start" mode? SR also has one jumper difference (move jumper to ZC and H), correct?

      2) The TT connection between the aquastat and the SR can be low voltage thermostat wiring, right? Right now, I have a 14ga line on the SR's ZR, since that is shared with X2 (TT to aquastat will now connect to X1/X2 on SR), which is what gives me pause.

      3) Confirmed that no circulators are currently connected to the 8124.

      4) How does one bypass the low limit on the 8124? (is this switching it between "warm start" and "cold start"?) And can you help me understand what that means? (feel free to point me at documents to read ...)

      Thanks again, you're helping me understand what's going on. I appreciate your help!

      -FM

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      • #4
        Re: Boiler aquastat wiring question

        OK, I've found this thread in which a guy asks a similar question ...

        http://forum.doityourself.com/boiler...er-heater.html

        I think I'm getting the picture now, but let me confirm:

        1) If I want to leave the boiler in warm start mode to avoid potential leaks or other issues, I can leave the current aquastat as is and let it control the boiler as normal, right?

        2) Then, all the 503 really is, is a thermostat combiner / circulator starter. Three thermostat inputs come in, one output goes to the aquastat to let it know that at least one is calling for heat, and the aquastat acts as normal. The circulator will run when the corresponding thermostat calls via 503, and water will always be warm enough to circulate, via 8124.

        So, I change the 503 over to cold start mode, leave the 8124 in warm start mode, and the new connection between is a low voltage wire between X1/X2 and TT, and I should be good, is this correct?

        -FM

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        • #5
          Re: Boiler aquastat wiring question

          Yes. but, I would get rid of the low limit and save yourself some money on the oil bill. There is no reason to maintain temperature in the boiler. Better yet would be to get hold of a Taco PC700 boiler re-set controller and modulate your boiler temperature based on outside temperature and load. Save the big bucks
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          • #6
            Re: Boiler aquastat wiring question

            Thank you very much, you've given me great and helpful information!

            -FM

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            • #7
              Re: Boiler aquastat wiring question

              On a cast iron boiler, you should not disable the low limit.

              If you disable the low limit, you will save money short term, but loose in the long run. Fuel oil condensate is difficult and messy to get out of a boiler when it has condensed for long; and it will shorten the life of your boiler.

              If you want on-demand heating, the best way is to install a low mass on-demand boiler (there are several available these days).

              The modulating controls are good too, but only if installed properly. We've rewired many after another "professional" installed them, and even pulled a few out completely due to the owner being disgusted with what they got for their money, and not wanting the thing in their building at all anymore.
              Last edited by radar_40; 03-01-2010, 04:49 AM.

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