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Thread: Boiler not operating within Hi Lo limits

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    DIY Junior Member ut7351a's Avatar
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    Default Boiler not operating within Hi Lo limits

    I have a Teledyne Laars Max D100 Boiler w/ indirect hot water. It is a cold start boller. It has separate Hi Lo limit controls. Hi limit set at 200F, Lo limit set at 180F. Problem: When thermostat calls or heat, boiler heats up to about 165F & burner cuts out. As water circulates boiler temp starts to drop. When boiler temp drops to about 155F, burner kicks back in & heats up to about 165F again & continues back & forth until thermostat is statisfied. Why isn't boiler operating between the Hi Lo control settings?

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Does it have an outdoor reset controller? If so, it adjusts to the load and outside temperature and overrides the manual settings.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Junior Member ut7351a's Avatar
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    No Outdoor controller.

  4. #4
    In the trades Dana's Avatar
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    This boiler probably has a safety high-limit aquastat in addition to the operational high/low settings. If the safety is set (or has failed) to 165F (lower than the operational high limit) it would exhibit this sort of behavior- kick off at 165F, back on again at 155F, repeat...

    Is this the boiler in question?

    If it's this series or similar and you incorrectly assumed the safety aquastat to be the low-limit, that could be the whole issue. (although 165F is way lower than the 180F you set it to.)

    What model aquastat(s) does this beast have?

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