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The Leader Runs In Lag

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  • The Leader Runs In Lag

    There is a church that had 2 Burnham basic cast iron boilers tied to a baseboard system in primary/secondary setup. The second boiler inline for the primary loop began to leak. It was decided by the church and installing company to put in a larger 2 stage boiler (Lochinvar Solution) and run the system with the new boiler as a leader. They also have a Tekmar 262 boiler control on the system.

    Call came to me yesterday that the temperatures in the church are running low and the lag boiler is doing all the work. I will need to explain to them that the 1st boiler in the loop is throwing heat at the 2nd boiler and that is causing the boiler desired to be the leader to operate in low fire all the time.

    As for the fix without a repipe? I am picturing a relay switch off the high fire side of the new boiler and an aquastat sensing the primary loop return water. This way the lag boiler can only fire if the leader is in high fire and the system water must also be at or below 140F.
    Last edited by Jones Mechanicals; 11-04-2011, 03:47 PM. Reason: spelling

  • #2
    Re: The Leader Runs In Lag

    Was the Tekmar added with the new install? If so, how was it controlled before? You want the new boiler to be primary right? Why not switch the wiring at the Tekmar and make the Burnham the lag? Without seeing how it's piped at the boilers I don't see why that needs to change.

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    • #3
      Re: The Leader Runs In Lag

      Originally posted by plumberscrack View Post
      Was the Tekmar added with the new install? If so, how was it controlled before? You want the new boiler to be primary right? Why not switch the wiring at the Tekmar and make the Burnham the lag? Without seeing how it's piped at the boilers I don't see why that needs to change.
      Yes the Tekmar was existing and the new boiler is set as the lead on the Tekmar with rotation turned off. The problem is in the order of the pipes.

      Here's the sequence. The Tekmar kicks in the new boiler, which by default runs the first 5 min. in low fire. The Lochinvar then goes to high fire as it should. Now the Tekmar calls for the second boiler to fire. The second boiler is in lead of the Lochinvar as to water flow. So when the second boiler heats up, its temperature gain then goes into the Lochinvar and throws it into low fire. If the boilers were plumbed into the primary loop in the reverse order there would have been no issue.

      Now with the additional controls the Burnham can only fire when 1. The Tekmar is calling. 2. The Lochinvar is in high fire mode and needing more heat. 3. The primary return temperature is 145F or less, verifing that the system does need the additional BTUs.

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      • #4
        Re: The Leader Runs In Lag

        Okay!.. NOW I get it

        I would almost want to reverse the piping arrangement before adding the relays but that is the easier solution.

        You know, the next guy that comes in behind you to service this system is going to be scratching his head wondering just WTF you were thinking

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        • #5
          Re: The Leader Runs In Lag

          each boiler should be piped into the a primary loop separate

          that way you do not have the problem of the water from one boiler going into the other like this




          Charlie

          My seek the peek fundraiser page
          http://observatory.mountwashington.o...nal&fr_id=1040


          http://www.mountwashington.org/weather/conditions.php

          new work pictures 12/09
          http://public.fotki.com/hvachawk/

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          • #6
            Re: The Leader Runs In Lag

            Each boiler is piped into the primary loop seperate and on close T. It's the nature of these two boiler types and in this order that caused the issue even though the plumbing concept is correct. Had these been 2 standard 80% units or 2 mod/cons there would have been no issue.

            To bad the company didn't want to pay me to repipe it for them...

            Yeah I can't wait for a follow-up tech to go in there and fiqure out what's going on. He'll rip it all out and rewire it. Then get the failure calls and put it back the way I have it...lol

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            • #7
              Re: The Leader Runs In Lag

              was there a check valve on each boiler supply pipe this would stop the flow from the other boiler
              Charlie

              My seek the peek fundraiser page
              http://observatory.mountwashington.o...nal&fr_id=1040


              http://www.mountwashington.org/weather/conditions.php

              new work pictures 12/09
              http://public.fotki.com/hvachawk/

              Comment


              • #8
                Re: The Leader Runs In Lag

                Originally posted by HVAC HAWK View Post
                was there a check valve on each boiler supply pipe this would stop the flow from the other boiler
                Not one check valve in the system.

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                • #9
                  Re: The Leader Runs In Lag

                  Originally posted by Jones Mechanicals View Post
                  Not one check valve in the system.
                  thats the problem then
                  Charlie

                  My seek the peek fundraiser page
                  http://observatory.mountwashington.o...nal&fr_id=1040


                  http://www.mountwashington.org/weather/conditions.php

                  new work pictures 12/09
                  http://public.fotki.com/hvachawk/

                  Comment

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