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24V C Wire Adapter Help

Hey everybody,

I recently got a Honeywell Home thermostat and when I installed it, it kept flashing on and off. Turns out that the furnace couldn’t give it enough power on its own, so I just got a 24V Power Adapter that I will plug into an outlet near my furnace. I have single pipe steam heat, with no AC.

I have two questions: will connecting the two wires to the C terminal and the RH terminal, along with the W wire from the furnace to the thermostat, give it enough juice? The instructions on the adapter say to connect the wires to the C terminal and the RC terminal, which confused me since I don’t have cooling. 

My second question is if I do connect the adapter wires to the C and RC, along connecting the RH and W wires from the furnace to the thermostat give me enough power, and is one option better than the other? Or am I completely off base? Thanks guys! I’m still learning haha

I can provide pictures if that is more helpful


  • Big Ed_4
    Big Ed_4 Member Posts: 1,884
    If there is a jumper between Rc and Rh remove ... You need 4 wires , The power adaptor conect to Rc and C and would power the thermostat the Rh and W will control and turn on the heat
    I have enough experience to know , that I dont know it all
  • thisoldhouse
    thisoldhouse Member Posts: 2
    Thanks Ed! There is currently a jumper connecting those two so I will remove that. Sounds simple enough, I will do just that.