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Why is my high limit aquastat behaving like a low limit aquastat?

ericmhurtado
ericmhurtado Member Posts: 54
in Thermostats and Controls
Hello, I am having an issue with the high limit aquastat. As you can see from the attached pic, I have disconnected the low limit aquastat wires from the burner because I no longer need it as I have installed a electric heat pump water heater. Why is the high limit aquastat, a honeywell l4006a, clicking and turning on the burner even though there is not a call for heat? Thanks in advance for all of your advice.

Comments

  • STEVEusaPA
    STEVEusaPA Member Posts: 6,505
    It's broke, short in the wiring, or wired wrong.

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  • ericmhurtado
    ericmhurtado Member Posts: 54
    Probably wired wrong to the oil primary control. In the attached pic, the high limit is connected to the same terminals as the steam thermostat, but according to the honeywell wiring diagram, the terminals should be for a thermostat and a temperature limit control for tankless heater only. So where else can I wire the high limit to? To those two unused terminals above it?
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,505
    The high limit is a safety control and should not be wired to the T-T. It should be wired in series to break power to the burner when high limit is reached.

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  • ericmhurtado
    ericmhurtado Member Posts: 54
    Thanks for the quick response @STEVEusaPA
    How can I wire the high limit in series?
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,505
    edited February 2019
    I just realized this is steam. Is there a hydronic loop too? If not I don’t understand the need for a high limit.
    Pictures from a little farther back would help

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  • ericmhurtado
    ericmhurtado Member Posts: 54
    Yes @STEVEusaPA there is also a hydronic loop. The thermostat for the loop is wired to a Honeywell ra89a relay and so are the circulators. I will send pics soon. Any idea how I can wire the high limit correctly?
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,505
    Send pics. I’ll draw up a diagram tomorrow.

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  • ericmhurtado
    ericmhurtado Member Posts: 54
    edited February 2019
    I have attached additional pics. One is of the hydro loop with the high limit on the boiler pipe, one circ on the supply and the other red circ on the return. The other pic shows the ra89a relay connections and another one shows how it’s wired.
  • ericmhurtado
    ericmhurtado Member Posts: 54
    Because the high limit is wired to the tt on the oil primary, the r7184p, is the reason why it’s behaving like a low limit. I don’t need the tankless coil, and as a result, the low limit, so I have disabled this aquastat. I would need to rewire the high limit to make it a cold start boiler. Thanks for all the helpful advice with this discussion.

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