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  1. #1
    Join Date
    Nov 2008
    Posts
    16

    Aquastat ignores LO setting?

    In the last year I had new heating equipment installed (AS Air handler blowing over a hot water coil). This replaced a single baseboard zone in the upper level. That level is fooled into two zones by master/slave thermostats and a damper @ the A/H. There remain two independent baseboard zones in the lower level. The boiler and its aquastat were not replaced. The boiler also provides HW to the Kitch&bathroom via an internal coil. There are three new flo valves (BG), three new pumps (Taco) for the three zones with a new ARGO panel
    The boiler sends the HW to the attic where the AH/coil is.


    I feel like there's a problem: The boiler's aquastat is set for HI:180 and LO:130. If the heat is turned off the boiler will not fire until the LO temp is hit via normal dissipation. This is good. If HW is called for by, say, the bathroom the boiler will not fire until the LO is hit via demand. Also good.

    But, when the heating zones call for heat the boiler will fire as soon as the boiler temp dips below 180 or if the current temp (@ call time) is already below the 180. This just doesn't seem efficient or good for the boiler if it has to fire up so often. Just wait until the outside temp is 20. Is this normal? I can't remember if the boiler behaved this way prior to the new equipment. I don't think so. Do you need more info? I don't want to have the HVAC guys back unless I can be reasonably sure they won't point the finger at the boiler/aquastat (maintained by the oil company).

    the boiler: WM Gold
    Aquastat: Honeywell Tri-Aquastat L8124A,c or L8151A

    thanks, Bryan



    Equipment:
    WM Gold w/ QB480 pump
    Argo panel
    BG Flo valves S/A 3/4
    Taco circs 007-F5
    Boiler Honeywell Aquastat L8124AC/L8151A

  2. #2
    Join Date
    Aug 2008
    Location
    brampton
    Posts
    9
    Could be the aquastat is defective, or maybe even your system is inproperly piped from the boiler get someone to look at it.

  3. #3
    Join Date
    Oct 2008
    Location
    Bethel Park, PA
    Posts
    103
    This seems perfectly normal to me. The boiler low limit is set to maintain boiler temperature for domestic hot water usage. When the Thermostat input is energized, the low limit is essentially ignored and the high limit setting is now the one that takes over control. The differential on the high limit on the 4125 is 10* so if the limit is set to 180* , when the temp drops to 170* the burner will fire again.
    I don't know which argo panel you have and I am not familiar with them. You should have some sort of other control to send different water temps to different zones. You most likely dont need 180* water to your hydroair zone, while you may to the baseboard zone. You would also benefit from an outdoor reset control so the boiler temps aren't 180* on a 30* day.

  4. #4
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,876
    Your boilers aquastat is working the way it is suppose to.

    Anytime there is a heat call, the aquastat uses the high limit to control water temp.
    During a heat call, the low limit only stops the circ from running to prevent you from running out of domestic hot water. It has no other function during a heat call.
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  5. #5
    Join Date
    Oct 2008
    Location
    Bethel Park, PA
    Posts
    103
    Wow, that been there doesn't miss much does he!!!

    I forgot the part about the low liimit controlling the pump during a heat call.

    Thanks for the backup!!

  6. #6
    Join Date
    Nov 2008
    Posts
    16

    10Q VM

    Right down to it, thank you. I'll digest this more; there's so much said and then go for competing quotes from the berler & AC folks.

    And then! the A/H and its peculiarities. but that's a later post.

    thanks again, B

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