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  • Circulating pump cuts out too soon

    Have a basement radiator that doesn't get as hot as the other rads as it is a greater distance from the boiler than the others. Boiler is a Slant Fin GG125 with Aquastat L 4081 Controller. Can I set the controller to make the pump run a little longer? If not, any suggestions?

  • #2
    Re: Circulating pump cuts out too soon

    Bleed the radiator, there should be a vent on it to let air out, if other radiators on the same zone are working, it's probably not the circulator.

    Without confusing you, but especially if this is a mono-flo system air will easily stop a single radiator from heating while the rest still work.

    Where it's in the basement, if that doesn't work, you may have to flush the zone if any part of the supply/return is above the height of the radiator.

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    • #3
      Re: Circulating pump cuts out too soon

      To clarify - The system is a two pipe return loop. The basement rad eventually gets heat especially in colder weather when the boiler is running alot, but the pump usually cuts out before the new hot water makes it that far. (especially in fall and spring) If the pump ran for another minute or two that would probably do the trick. Any ideas?

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      • #4
        Re: Circulating pump cuts out too soon

        Still bleed the radiator, it might not work, but it won't hurt.

        A mono-flo is still a two pipe system (all hydronic, hot water boilers are, except maybe some obscure gravity sytems), but each radiator branches off the primary loop on a mono-flo, where a regular system is a series of radiators in a loop with no primary between them, no branches, they're each a part of the actual loop.

        It could also be connected to a split loop, if so, you could adjust the valves at the split, assuming there are any, but that'd be a but confusing to 'splain online if you don't understand.

        That said, if the basement doesn't have a separate thermostat and the radiator is connected to another zone, you may have to have a heating guy or plumber take a look if you can't find a split, you could need it separated into it's own zone with a circulator, relay and T-stat of it's own.

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        • #5
          Re: Circulating pump cuts out too soon

          I'll address you as Duck, thank-you for your patience, time and assistance.
          My initial question... Can I set the controller to make the pump run a little longer? When I jump the controller and run the pump manually for a few minutes - it does the trick. I've read that some systems in Canada (Toronto) don't cycle the pump - It just stays on... Ours is set at Hi- 180° and a low set to 120°. Just as the hot water gets going it shuts off. The pressure is about 12 PSI - but I can't understand why the temperature gauge doesn't appear to go above 110°.
          I've bled all the rads - no air. It's an old system with a newish boiler 5 years ago, 3 speed Grunfos pump (set at middle speed). See attached image, similar to the system we have. One zone. It's pretty cold for the last few days so everything's working well. As soon as this cold snap is over all the rads will keep nice and warm except the rad at the end it will stay luke warm. I really hate spot heating that room with electricity.
          Does any of this help?
          Attached Files

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          • #6
            Re: Circulating pump cuts out too soon

            Bruc, the circ won't stop running until the T-stat is satisfied, unless somehow this is wired differently, like feeding a secondary system for radiant flooring.

            If the radiator at the end is piped exactly like your diagram, then you have a weird hybrid mono-flo, where the last radiator is part of the primary loop instead of being another parallel branch in the loop.

            In a hydronic system, the water is always going to seek the path of least resistance, which is apparently everything but the last radiator in your diagram.

            In other words, the water is meeting less resistance through the radiators before the end one.

            This could mean the original installer didn't install mono-flo tee's, installed them wrong, or something similar, which would ordinarily restrict flow in a way to allow less resistance to the primary loop and allow flow through the last radiator.

            If these are old steam radiators on a two pipe system, try tightening the 1-1/4" valves to restrict flow and encourage flow through the primary.

            If this is the case, you'll have to tweak each one to get them to work right.

            If not, you'll probably need someone to look at ti first hand.

            Last note, please, don't mess with the wiring or boiler, the things I've mentioned so far are good to know as a homeowner for standard maintenance, but you don't want to short something at this hour with the weather like it is.

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            • #7
              Re: Circulating pump cuts out too soon

              Thank you for your advice. I agree, messing with the system now isn't very wise. I've been living with the cool room for a few years and will sooner or later get it figured out. House built in the 20s. On closer inspection - I think this rad appears to be what you call a parallel branch on the loop. There are two 2" loops with returns branching off the main feed pipe. This one is 1" copper off the main pipe kinda on it's own - Maybe getting it zoned with it's own t-stat is the answer? As for the rest of the house - You can't beat the big old cast iron rads.

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              • #8
                Re: Circulating pump cuts out too soon

                you will have better luck if the return is changed to the opposite end. in other words return should came back from last rad not first as it is now. that may be impossible without a lot of work. if return had been flipped all runs would be the same length or close. if it was me i would post this at www.heatinghelp.com ask questions. breid...............

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                • #9
                  Re: Circulating pump cuts out too soon

                  do all of the rest of the rads have valves on them? if so do as duck said. turn all the valves back(gently) until basements heats up. then tune each one. copper fin heats differently than cast. there is a learning curve. take your time this has been messed up for years. breid............

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                  • #10
                    Re: Circulating pump cuts out too soon

                    Doesn't the Honeywell L4081 have a separate pump control aquastat? Or am I thinking of a different controller?

                    You could lower the pump cut on temp so it would circulate longer.

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                    • #11
                      Re: Circulating pump cuts out too soon

                      Bruc, after you finally mentioned that the radiators are cast iron and the primary is 2" and this is an older home, I could almost guarantee you have a two pipe steam conversion to hydronic.

                      As one individual above reiterates, just tweak the valves on the radiators closest to the boiler until you create enough resitence to encourage flow to the basement radiator.

                      Unless a detail has been missed, or as Plumberscrack suggests where you might have something more complicated for wiring or circulation (which I can't see for this application, but I've seen some wacky homeowner installs in my time), this problem is very straightforward.

                      Adjust the valves on each radiator, slowly, until you get results also make sure the valve on the radiator in question is wide open..

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                      • #12
                        Re: Circulating pump cuts out too soon

                        An L4006 or 6006 strap on aquastat installed on the feed near the radiator and running low voltage wiring back to the TT terminals on the circulator relay ( in parallel ) will solve the problem, though the one will overheat slightly.
                        sigpic

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                        • #13
                          Re: Circulating pump cuts out too soon

                          If the problem is circulation, wouldn't that cause the other radiators to overheat the space?

                          Actually, I guess that depends on whether you bypass the T-stat with the aquastat, but if you don't, the T-stat will kill the boiler anyway.

                          What am I missing here?

                          I'm all Vinny Barbarino'd now.

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                          • #14
                            Re: Circulating pump cuts out too soon

                            well yes duck it will. but he will have a warm basement. breid...........

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                            • #15
                              Re: Circulating pump cuts out too soon

                              Oh yes very, very warm.

                              I guess the gist would be to wire the aquastat to stop the circulator when the feed temp reaches a point after the boiler is off, but that wouldn't stop the heat from running in the other radiators in the same loop.

                              I just think it's simple matter of the path of least resiistence, tighten some valves, good to go.
                              Last edited by DuckButter; 12-07-2010, 09:00 PM.

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