Click here to Find a Contractor in your area.
Welcome! Here are the website rules, as well as some tips for using this forum.

If you've found help here, check back in to let us know how everything worked out.
It's a great way to thank those who helped you.
Need to contact us? Visit

Boiler Control Issues

rossihvacrossihvac Posts: 2Member
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


  • unclejohnunclejohn Posts: 1,372Member
    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.
  • rossihvacrossihvac Posts: 2Member
    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.
  • HVACNUTHVACNUT Posts: 2,172Member
    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.
Sign In or Register to comment.


It looks like you're new here. If you want to get involved, click one of these buttons!