Boiler not working right, need help

Discussion in 'Boiler Forum' started by zx7ninja, Jan 25, 2013.

  1. zx7ninja

    zx7ninja New Member

    Jan 25, 2013
    Hi guys. It's damn cold, 10 or so during the day, much colder at night. Bad time for boiler problems. But i've got 'em.
    No idea what's happening, but from all the reading around it could be short cycling, but I don't know enough to say.

    Here's the details:
    Natural gas fired Teledyne Lars jvt-100c Was told it's the original boiler from house cinstruction in 1986. If true, it's almost 30 years old. It sure looks it. 100k/80k btu

    House sq footage - 1880 plus additional 1000 in basement. Basement is not finished, but there is 1 small baseboard down there. Can't turn it off, it's on the same zone as my den. (I do plan on finishing the basement, roughly 750 sq ft o fit, so please take that into account for future plans)

    Hot water baseboards in the house, 3 zones. 2nd floor, 1st floor sans den, and den+basement.

    The house is pretty tight.

    Now, the problem:

    I woke up the other day to find that the house was in the mid to high 50's. Thermostats all set to 67. Boiler was NOT on. Chalked it up to a one time mess up. Throughout the day, the house wouldn't even break 61.
    I noticed the thermostats (one for each zone) would all say "Heat On" but in fact the boiler was not running. So....I spent 3 hours in the basement, just watching it. (basement is not finished, but it is tight, and comfy with a jacket on)

    What I noticed, is that the boiler WILL fire, but only run for 2-3 minutes before kicking back off. All 3 thermostats still constantly say heat on.

    The water feed and return pipes for all 3 zones are scorching hot, and all of the baseboards are getting warm. But NOT hot like they used to. Just warm.

    I have NEVER had this issue. I called the only local tech willing to come look at it, only to be told that the office didn't tell him it was gas, he's the oil guy, and can do nothing for me.

    He did say that natural gas doesn't work in cold weather, that's why they invented oil boilers. Really?:rolleyes:
    Well, I gues he IS an oil guy....

    Anyway, not sure what's happening. It just won't stay fired. Maybe the super low temps here are more than it can handle? Possibly due to age/wear? And it hits internal temps long before the rooms heat up?
    Of course, since I am a newb at this, I could just be talking nonsensical.

    Short-cycling seems to fit, but the question is why?

    And, based on the age of the boiler, maybe just replace it? My local HD has a slant fin sentry 120k btu marked down to 1300, 1 left in stock. I got estimates of 500 bucks for the labor, so 2k or less for a new boiler. But I have no idea if that's good or not, or what OTHER parts I may need to make it work, pushing price to 3k, 4k, 5k, or more.

    So, my questions are two-fold. 1st, what could be happening with my current setup? I need some darn heat!

    2nd, based on the age and issues, you think I should just replace it? Is the slant fin sentry 120k boiler good? Is it enough for my 1880 sq ft main area + 750 sq ft basement (once finished)? Is the price good, and what, realistically, should I expect to spend?

    BTW - my gas bills are outrageous. My rates are first 30ccf .8108 per 31ccf and up .5404 per, and my bill ranges from 275-300 in the milder fall early winter, to 400-500 monthly november, december, january, and february. Seems like I am paying a LOT more than I should be.

    Some forums I was reading, a guy had a 150k btu and a 3000 sq ft home, paying 135 monthly, AND his rates are higher than mine. What the hell.

    Anyway, enough rambling. Please, educate me here.:cool:

    EDIT - Wanted to mention that the boiler is NOT handling HW duties. I have a separate nat gas HW heater for that, and it seems to be working perfectly. SO this is for heat only.
    Last edited: Jan 25, 2013
  2. BobL43

    BobL43 DIY Senior Member

    Mar 25, 2011
    Retired Industrial Automation controls/tech s
    Long Island, NY
    First of all, I am not a plumber or HVAC guy, but from your description of the problem, it sounds like your circulator pump or zone valves (or frozen line somewhere?) are not allowing flow of water from and back to the boiler. You said the boiler heats up, and shuts off after 2 to 3 minutes.To me that sounds like the boiler is reaching its setting and just shuts off, having satisfying the aquastat temp setting. What does the boiler temperature gauge show? Is the circulator running at all?
    Last edited: Jan 25, 2013
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  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Sep 2, 2004
    Retired Systems engineer for defense industry.
    New England
    Your existing boiler is probably 2x oversized, so do not just buy a higher powered one without having someone run a manual j heat loss calculation on your house. It sounds like a circulation problem...could be the circulator, could be an air lock, could be a controller problem where it's not actually turning the circulator on. WHen new, your current boiler was 80% efficient at its best. The newest ones can be in the upper 90% range. NG works just fine in cold weather - that oil guy is either full of it or pulling your leg. If anything, oil can turn to a waxy sludge if it gets really cold and really mess up the inlet supply line - NG just keeps flowing.
  5. BobL43

    BobL43 DIY Senior Member

    Mar 25, 2011
    Retired Industrial Automation controls/tech s
    Long Island, NY
    I think the oil guy was talking about propane maybe, and that only happens with small tanks with too small surface area that get cooled down with the combined cooling effect of the gas boiling off to evaporate to gas and extremely low outside temps. I heat with oil, as its the only fuel available by me that I don't have to shovel or clean ashes.

    Just had the basement 275 gallon tank replaced after 41 years. Was worried it would rust out and leak. AMAZING how much sludge was in there, and not just at the bottom of the tank either. They emptied and cut the tank apart in the basement. Very neat job, I was amazed; they must have done this before:p
  6. Dana

    Dana In the trades

    Jan 14, 2009
    The described symptoms could apply if it's plumbed primary/secondary the zone pump(s) could be working, with the primary pump kaput. The boiler is probably fine and hitting it's high-limit quickly with only the sloshing minimal flow induced by the secondary loops going through the heat exchanger. In some boilers the primary loop pump is inside the boiler, but from the exploded diagram that's not the case here.

    Fix the flow and you'll more than likely fix the problem. Fix it before swapping in a boiler, or anything you swap in would behave similarly. The boiler might be old, but it's obviously working. It's extremely unlikely that the low flow is due to the heat exchanger scaling up, or you would have noticed tepid radiation long before now, but if in fact it's scaled up, it could explain the ridiculous gas bills, since a short-cycling 80% efficiency boiler that's hitting a 200F high limit on every burn would have huge standby loss. But if it's the pump impeller corroded to the nubbins, that could have nearly identical symptoms (and costs.)

    This system needs to be looked at by somebody who can properly diagnose the problem, not by somebody dying to sell you a boiler.

    If replacing the boiler it's important to right-size it for the actual heat load. A typical 1900' (+ semi-conditioned basement) code-min 1986 house in southern New England with U0.6 windows and cheap R19s in 2x6 construction (or even R13s in 2x4) will have a heat load of under 50,000BTU/hr @ +5F (a typical 99% outside design temp for CT, but find a nearby city and compare.) Many houses that size & vintage that are fairly tight, with U0.50 or better windows will come in under 30,000BTU/hr. If your house is exceptionally leaky to air infiltration or has a ridiculous amount of glass, or single-pane glass (was that code-legal in '86?), it might as high as 75,000BTU/hr, but in a house that drafty the solution isn't a bigger boiler, it's retrofit weatherization (including air sealing and insulating that foundation/basement!) If you have a lot of work to do on those fronts, size the boiler for the "after" picture, not the as-is condition. But I assure you there's no WAY the heat load was as high as the 80K output of that boiler when it was new, and going with a boiler with more output than 80K would be a mistake- even replacing it with another 80K boiler would be a mistake, since your heat load is probably under 50K, and reducing it to under 40K is probably not going to be very expensive, and would add a lot to comfort.
    If replacing the boiler, right-sizing it for the actual heat load is important for both efficiency and comfort. UP sizing a boiler is almost never the right thing to do- it costs more up front, has higher maintenance problems due to cycling frequency, and comfort issues related to overshoots. Whenever possible, DOWN size it to something less than 1.25x the actual heat load (sometimes it can be measured by fuel use, but probably not in your case), or no more than 1.15x the calculated heat load from a Manual-J or I=B=R type heat loss calculation.

    For comparison purposes, I live in a comparable climate in Worcester MA (99% design temp = +5F, but it was -2F yesterday when I got up), in a ~2400' (+ ~1500' of insulated basement) 1920s 2x4 framed house, with single-pane double-hungs + storms, and my heat load is well under 40,000BTU/hr. There are known gaps in the insulation, and most of the roof/attic is only ~R20 (some foam, some fiber) between 2x6 rafters, and in some places it's less. My heating system is radiation-limited to ~45,000BTU/hr max at the water temps I'm running, and it does just fine keeping up well into negative-digits (it hit -8F once last winter, and though the recovery from the relatively shallow setback was slow, it didn't have any problem getting back to 68-70F indoors before the outdoor temps warmed up to -5F, let alone +5F.

    Natural gas NEVER works in cold weather, and oil NEVER has jelling problems at low temp, are you kidding? That's why they never use natural gas in Canada... or Russia... and they just export all that crap to warmer sucker-countries! :rolleyes:

    The kind of BS that comes out of boiler-tech's mouths sometimes! Do you have to pass the idiot-test, no rokkit syintists 'llowed to install boilers in New England? Just yesterday a friend of mine was told by the guy installing the replacement her defunct 70 year old steam boiler that she needed to get rid of the programmable setback thermostat, because setback operation puts too much stress steam boilers. (Show me the data on that one, or at least a good narrative that doesn't violate the laws of physics!)
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