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Loop HW System Short Cycles

Mike T., Swampeast MO
Mike T., Swampeast MO Member Posts: 6,928
in THE MAIN WALL
Not terribly unusual for a boiler to cycle <I>during</I> a call for heat--such essentially means that the boiler is putting out more heat than the emitters can liberate.

However, circulation through the emitters <I>shouldn't stop when the thermostat is still calling for heat</I>. This makes me think that your system is improperly wired.

Excessive cycling during a heat call could also be the result of too low an aquastat setting. Lower system temperature means lower emitter output. This would be especially noticeable during recovery from thermostat setback as such requires a lot of "extra" energy to increase the heat level.

180F is the "typical" aquastat setting with fin baseboard. If significantly below, I'd suggest increasing to 180. If already there, you might want to increase to 200 or so (higher temps can be used, but unless the emitters are way too small for the job they need to do, I'd suggest using less setback before increasing the aquastat setting much above 180).

One other thing regarding setback. As the weather gets colder, it takes longer and longer to recover from the same amount of setback. In extremely cold weather it can take nearly the full output of your emitters just to <I>maintain</I> space temperature--even at a reduced thermostat setting. That means there can be very little "extra" energy available to raise space temperature. If you start noticing problems in extremely cold weather <I>and you're using daily setback</I>, reduce the amount of setback (or even eliminate) and your problems may well disappear.

Comments

  • Mel_3
    Mel_3 Member Posts: 15
    Loop HW System Short Cycles

    This was first very cold day with 18 month old system and there was clearly a problem. Seems at times the thermostat was calling for heat (little flame in the stat window) but the (standing pilot gas) boiler was off. Air temperature was clearly below setting. I know of short-cycling with steam, but this one has me puzzled!?

    Thanks.
  • Mel_3
    Mel_3 Member Posts: 15


    I should add that at these times the circulator shuts off and the fin radiators cool down.
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