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high low limit switch

Andre Member Posts: 11
Why would the high limit be set higher on the boiler for the tankless coil set up and lower for the indirect set up?
Does this affect my heating zones, what would be the preferred temperature for the heating zones in hot water baseboard. Does one take from the other. The boiler only knows high, low, and not what its heating the water for, is this whats happening in a indirect water heater control setup.
PS. My Crown TZW125 came with the the L8124 factory set at 210*high and 180*low Why? It cycles at very frequent intervals.

More help please


  • Andre
    Andre Member Posts: 11
    Boiler settings

    I installed a Crown Model TWZ125 water boiler and I would like to know what is the best high low settings to make. Here are my perticulars. The boiler came with a tankless hot water coil which I'm not useing. Instead I installed a 40 gal mega - stor indirect water heater. The aquastat relay is a Honeywell L8124A,C. The boiler is wired for a priority setting for the Mega Stor. Question: Would the high low settings be different if using the tankless heater only, and what would they be? And: What should the settings be with the indirect mega stor, with the tankless heater not piped. Also on the aquastat there is a differential setting, where does this come in.
  • Al Letellier
    Al Letellier Member Posts: 781
    aquastat settings

    Depending where you live, set as follows; Here in Maine, with a coil, HI 200* LO 180* differential 20 or higher. With an indirect HI at 190* LO set to boiler manufacturers recomended low limit (usually 120-130*)
    The differential only comes in to play with a tankless coil. Normally a 10* differential is set by the control maker. During hot water call only, the boiler maintains low limit temp and will drop 10* on a hot water call and will start the burner and run the temp back up to low limit setting. By adjusting the differential up to say 25, the boiler will drop 10* below low limit fire the boiler, and run up 25*, or 15* over the low limit. This keeps the boiler hotter for the domestic coil, gives a longer "draw down" before starting the burner and gives the burner a longer run cycle, which we all know is more efficient that a lot of short ones.
    If using an indirect, leave the differential at 10. You want the boiler to run as little as possible to save energy. Where you live and how well the system is sized will determine how high to set the high limit. It gets damn cold up here and not all systems are properly sized and/or installed. Hope this answers your questions. Good luck.

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  • Weezbo
    Weezbo Member Posts: 6,232
    disregarding flow rates and heat loss delta t for a momment

    why not hire someone to stop in and start the boiler for you properly? for now you might turn down the low limits to 145 and then turn down the high limit to170 . ...how to?, manually open all the zones, turn the recirc on,by itself with the boiler off, when the temp drops to around 160 ish then dial it down.and turn it back on...take two asprin and call someone in the morning...
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