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Thread: Issue with competing zones shutting off boiler

  1. #1
    Sr. Systems Engineer, Biotech
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    Default Issue with competing zones shutting off boiler

    Have a situation with a heating system. The Burnham boiler is about 20 years old, tankless, forced hot-water baseboard, oil-fired system. There are three heat zones each with their own thermostat, two circulator pumps and 2 zone valves.

    When the system was originally installed, there were 2 zones with 2 circulator pumps and there were no zone valves. One circulator pump for level 1, the other for level 2. No problems were ever experienced.

    The attic was turned into living space and a 3rd zone added. For the 1st level, nothing changed; one circulator pump is dedicated to it. For the extra zone that was added, the plumbing circuit for the second level was branched off and 2 zone valves were added. The second circulator pump is now used to feed the 2nd level and attic. There is no issue with how the plumbing is configured. All of the work to add the 3rd zone was performed by the oil company.

    All thermostats are operating properly and are level and when there is a demand for heat from one zone at a time, there are no issues. I believe that a problem occurs when heat is demanded from more than one zone at a time. The system will run for 15 seconds then everything will shut off. After several minutes, it will turn back on again and run again for 15 seconds then shut off. This will continue until the temperature is reached. From what I witnessed, the boiler, circulator pumps and zone valves will all be off during this time. I have not poked around with a meter to start checking things yet and still need to determine the exact sequence in which this situation occurs.

    From what I see, when the 3rd zone was added, an additional box was added to the boiler and there is a spaghetti mess in and around it. I am extremely familiar with control systems but havenít spent more than just a few minutes looking at this to troubleshoot. In the long-term, there is talk of doing an addition which will require an additional zone. In the short term, Iíd like to straighten this mess out. Going with the plan that an additional zone will be added, would I be better off not dealing with this mess and just installing a new controller that could handle everything better? If so, would you have any recomendations? Thx.

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    If for some reason there isn't any circulation through the boiler - it will reach the high limit quickly and shut itself down.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    Sr. Systems Engineer, Biotech
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    It will exhibit this problem even when the boiler is up to temp and not running and just the circulator pump(s) are running.

  4. #4
    Master Plumber nhmaster's Avatar
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    The circ relay is wired wrong.

  5. #5
    Sr. Systems Engineer, Biotech
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    I had a chance to spend 5 minutes looking into it yesterday. All of the wiring is correct. The issue is that the 24V supply drops low when all of the zones are requesting. It looks like an additional 24V transformer was added to attempt to compensate for this, but was not large enough. This should be very easy to correct.

  6. #6
    Sr. Systems Engineer, Biotech
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    Just to follow-up, further investigation also found a temperamental zone valve, improper temp and differential settings in the aquastat controller and also an issue with the wiring between the aquastat and the relay box. The relay box is an Argo and the aquastat a Honeywell. The Argo was wired according to its own instructions, but the instructions were written as if it was to be installed with an Argo aquastat. They should have followed the wiring instructions for the Honeywell aquastat when adding in the Argo relay box.

    I will give some slack to the 3 different oil-companies that worked on this boiler for the intermittent zone valve, but the rest of it should have been caught.

    Aw well. All in fun, and I learned a few things along the way.
    Last edited by helix3; 12-17-2008 at 05:46 PM.

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