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Taco Switching Relay and Low Limit

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jrhughes
jrhughes Member Posts: 3
Our thermostats and circulators are connected to an SR506 relay by Taco. We have an L7224 triple aquastat on our keystoker K6.

The problem is our circulators run when heat is called regardless of being far below the low limit. So our rads are never getting hot.

Currently we have 120 coming in from the wall to the relay. The TT on the L7224 is connected to the end switch on the Taco. Nothing on ZC or ZR. It seems there’s communication to the furnace to say “make more heat” but nothing from the furnace (L7224) to the taco to say “Whoa, give it 30 degrees before you start circulating.”

And we need that.

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  • chapchap70
    chapchap70 Member Posts: 139
    edited November 2018
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    What are the low limit and the differential set to?

    Normally, if the low limit is set to say 150 and the differential is 10, the aquastat will cause the boiler to fire (if there already was a call for heat, the burner would already be running. See below.) and shut the circulator(s) off when the boiler water drops to 140 degrees . If the low limit is set to 130 and the differential is 25, the boiler on/circulator off will be 105.

    When there is a call for heat, the burner will operate on high limit so if your low limit/differential settings are not right, this would cause what you are seeing.
  • HVACNUT
    HVACNUT Member Posts: 5,887
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    You need to remove the low volt wires between TT and XX.
    Run 2 line volt wires, )#14 gauge) to ZR,ZC on the zone board and aquastat. I use red for ZR and blue for ZC.
    This will interrupt power to the circs when boiler temp drops to the low side setting.

    If your using a tankless coil, typical aquastat settings are 180 high-160 low. There should be a thermostatic mixing valve on the domestic hot.

    If you have an indirect water heater, you can go down to 145° low with a 10° differential for condensate protection if it's a cast iron boiler. I have no idea what a Keystoker K6 is.
  • chapchap70
    chapchap70 Member Posts: 139
    edited November 2018
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    It's a coal stove. I looked quickly at the manual and they did not use the ZC ZR terminals on the aquastat. They show an L4006 along with the 7224. I assume this is to trigger a control to shut off air for coal or run a dump zone if the temperature gets really high.

    Edit: Didn't see anything about a combo.