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Need help on a Lochinvar problem...

Tony_23
Tony_23 Member Posts: 1,033
What happens if you fire #2 on satge 3 by itself ? Does it "dump" then ? If it does, I'd look at input rate on stage 3 as compared to rated input.

If not, and it only happens when both are firing on stage 3, I'd look at combustion/intake air into the boiler room.

Comments

  • Ben_14
    Ben_14 Member Posts: 2
    Problems with a Lochinvar...

    I have inherited a problematic Lochinvar Copper-Fin II 990k BTU boiler. I took on this customer during the summer. After two calls for exhaust fumes this winter, I started to inquire about the history on the boilers. The boilers were installed in ’92 when the building was built. According to the customer, he has had intermittent problems with exhaust fumes in the boiler room since day one.

    After some experimentation, I discovered that the exhaust fumes only show up on cold days. On warmer days, when only one boiler is running, there isn’t a problem with fumes. I live in Virginia, so as you can imagine, there aren’t that many days when it is cold enough that both boilers have to run to keep up.

    There are two Lochinvar CHN0990 boilers installed exactly the same. Both boilers have 3 stages, are sidewall power vented, and they operate as lead/lag. Boiler #1 (lead) doesn’t seem to have a problem. However, when Boiler #2 (lag) fires its third stage, it starts to bleed exhaust fumes out through the barometric damper. It’s bad enough I can actually watch the barometric damper action change and feel the heat of the exhaust outside the mouth of the damper.

    In an effort to cover all my bases, I downloaded the Installation and Operation Manual on this boiler from Lochinvar’s website (God Bless the Internet). I read through the entire manual looking for potential problems. I checked all of the settings specified in the manual to eliminate possible problems. I even traded the exhaust piping trying to find some noticeable difference between the two boilers. No matter what I do, I cannot keep Boiler #2 from dumping exhaust gas when the 3rd stage fires. Does anyone have any ideas about what could be causing this problem?
  • combustion

    There seems to be a drafting issue. How clean are the heat exchangers if it is happening on high fire and the power vent is not pulling the exhaust out fast enough i would think the heat exchanger may be plugged up or there is not enough combustion air coming in. We went to servce the same boiler the other day, customer complained about a burning smell. I found a couple of dead birds inside the heat exchanger cooked to a nice crisp.
  • combustion

    There seems to be a drafting issue. How clean are the heat exchangers if it is happening on high fire and the power vent is not pulling the exhaust out fast enough i would think the heat exchanger may be plugged up or there is not enough combustion air coming in. We went to servce the same boiler the other day, customer complained about a burning smell. I found a couple of dead birds inside the heat exchanger cooked to a nice crisp.
  • Jeff Elston
    Jeff Elston Member Posts: 289
    Check

    I would check the fresh air inlets and the power vent sizing, as well as the B-vent vent connector sizes. Whats the make and model of your power venter?
  • tim smith
    tim smith Member Posts: 2,738
    Regarding copper fin II

    I have worked on quite a few of these, including the same application you explain. My first thought is the power venter is undersized. I think I understand from your description they are individually vented? correct? If so, I would be leaning towards a variable speed power venter w/ a static pressure control to vary blower speed based on vent pressure. This is how the ones I have worked on were set up. Nice design, Exhausto is the brand I worked with. 2nd, after you verify power vent sizing, the combustion needs to be checked, these can be a bit finicky to set due to the multiple stages on these. I would bet also the heat x needs cleaning and make sure to pull and wash the tube in tube burners, don't just brush, does not cut it. Call mfr of existing power venter and find out what capacity it has and then verify it with the installation. Good luck, Tim
  • Mitch_4
    Mitch_4 Member Posts: 955
    sounds like

    insufficient combustion air...without looking it up, you liste the input as 990,000 each, @ 50 cubic feet per 1000 btu, you need 990 x 50 x 2 cubic feet = 99,000.
    divide this by the cieling height to determine square footage of the room space. My guess is air is pulled in on boiler #2 to satisfy boiler #1.

    Reverse lead and lag, and fire, if the problem repeats itself when #2 fires, then it is an air supply issue.

    see it here all the time. not enough air, and they do not want cold air dumping in, and mechanical interlock is "too much money"

    Good luck
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