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  1. #1
    Join Date
    Feb 2009

    Default Restless Furnace

    Our house has hot water baseboard heating, driven by a natural gas furnace. There are 3 zones and 1 circulating pump. I have been noticing when the furnace kicks in, it is mixed in with short off intervals (about a minute). However, the circulating pump will be running the entire time.

    I have adjusted the swing setting on all 3 thermostats to the maximum, but still the same. Is this normal behavior or are we looking at costly repair soon? Thanks.

  2. #2
    Join Date
    Feb 2008

    Default Re: Restless Furnace

    This condition is known as "short cycling" and could be caused by any one of a whole host of things---but it's usually caused by a minor adjustment or small part that can be replaced easily.

    It's thus to your advantage to have a heating expert come in to service it, since you will waste a lot of gas until it's corrected.

    The correct term for your heating unit is a boiler, not a furnace.

    You can Google "residential gas boiler short cycling" (without the quotes) to get a long list of possible causes:

    1) Sometimes it's caused by the aquastat control on the boiler that is on the way out, or has dirty relays, or the settings are backwards---aquastat low limit should be 160 degrees & high limit should be 180 degrees.
    2) there is sometimes a flame sensor thermistor near the burners that sometimes goes defective.
    3) A faulty circulator may not be circulating sufficient hot water. 4) possible faulty ignition module in the gas valve.
    5) possible air blockage in the piping. 6) boiler could be overheating due to low water & locking out.

    If the condition has been present for years, the zone loads (radiators/convectors) may be too small for the size of the boiler.
    Last edited by NashuaTech; 02-02-2009 at 10:28 PM.

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