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Boiler Control Issues

rossihvac Member Posts: 2
I've been doing some searching and I haven't come up with any solutions so I figured I'd ask some experts. Customer has a Oil fired boiler that has a tankless coil with a Riello gun, 2 120 volt thermostats and 2 120 volt taco circs. Tying it all together is a Honeywell L4081B which is controlling the circs, controlling boiler temperature and hot water temperature. They would like to have low voltage thermostats installed so they can eventually install two wifi thermostats. My question is: How can i wire the honeywell L4081B to a Taco SR502 to provide the low voltage controls they want?

Thanks in advance


  • unclejohn
    unclejohn Member Posts: 1,833
    You should be able to wire the pumps to the Taco control and then wire the high voltage burner control through the TT dry contacts of the Taco control IF the amp draw of the burner does not exceed the load of the TT contacts. If the burner does you will need a isolation relay.
  • rossihvac
    rossihvac Member Posts: 2
    I don't think the dry contacts on the taco are rated for 120 volts, they are on the 24 volt side of the controller.
    HVACNUT Member Posts: 5,474
    Wire the SR 502 constant hot to L1.
    Wire the load side of the Lo setting on the L4081B (need the jumper in) to ZC on the SR 502 to make and break the circs on temp.

    The L4081B maintains the Hi setting so I hope theres a thermostatic mixing valve for the coil.